feat(channels): add custom account stats pricing rules

Allow channels to configure independent model pricing for account
statistics cost calculation, decoupled from user billing.

Backend:
- Migration 101: channels.apply_pricing_to_account_stats toggle,
  channel_account_stats_pricing_rules/model_pricing tables,
  usage_logs.account_stats_cost column
- resolveAccountStatsCost: match rules by group/account, then channel
  pricing, fallback to original formula when unconfigured
- Integrate into both GatewayService.recordUsageCore and
  OpenAIGatewayService.RecordUsage
- Update 8 account stats SQL queries to use
  COALESCE(account_stats_cost, total_cost) * account_rate_multiplier
- 23 unit tests for matching, pricing lookup, and cost calculation

Frontend:
- Channel edit dialog: toggle + custom rules UI with group/account
  multi-select and pricing entry cards
- API types and i18n (zh/en)

backend/internal/repository/usage_log_repo.go

@@ -28,7 +28,7 @@ import (
 	gocache "github.com/patrickmn/go-cache"
 )
 
-const usageLogSelectColumns = "id, user_id, api_key_id, account_id, request_id, model, requested_model, upstream_model, group_id, subscription_id, input_tokens, output_tokens, cache_creation_tokens, cache_read_tokens, cache_creation_5m_tokens, cache_creation_1h_tokens, image_output_tokens, image_output_cost, input_cost, output_cost, cache_creation_cost, cache_read_cost, total_cost, actual_cost, rate_multiplier, account_rate_multiplier, billing_type, request_type, stream, openai_ws_mode, duration_ms, first_token_ms, user_agent, ip_address, image_count, image_size, service_tier, reasoning_effort, inbound_endpoint, upstream_endpoint, cache_ttl_overridden, channel_id, model_mapping_chain, billing_tier, billing_mode, created_at"
+const usageLogSelectColumns = "id, user_id, api_key_id, account_id, request_id, model, requested_model, upstream_model, group_id, subscription_id, input_tokens, output_tokens, cache_creation_tokens, cache_read_tokens, cache_creation_5m_tokens, cache_creation_1h_tokens, image_output_tokens, image_output_cost, input_cost, output_cost, cache_creation_cost, cache_read_cost, total_cost, actual_cost, rate_multiplier, account_rate_multiplier, billing_type, request_type, stream, openai_ws_mode, duration_ms, first_token_ms, user_agent, ip_address, image_count, image_size, service_tier, reasoning_effort, inbound_endpoint, upstream_endpoint, cache_ttl_overridden, channel_id, model_mapping_chain, billing_tier, billing_mode, account_stats_cost, created_at"
 
 // usageLogInsertArgTypes must stay in the same order as:
 //  1. prepareUsageLogInsert().args
@@ -82,6 +82,7 @@ var usageLogInsertArgTypes = [...]string{
 	"text",        // model_mapping_chain
 	"text",        // billing_tier
 	"text",        // billing_mode
+	"numeric",     // account_stats_cost
 	"timestamptz", // created_at
 }
 
@@ -360,6 +361,7 @@ func (r *usageLogRepository) createSingle(ctx context.Context, sqlq sqlExecutor,
 			model_mapping_chain,
 			billing_tier,
 			billing_mode,
+			account_stats_cost,
 			created_at
 		) VALUES (
 			$1, $2, $3, $4, $5, $6, $7,
@@ -367,7 +369,7 @@ func (r *usageLogRepository) createSingle(ctx context.Context, sqlq sqlExecutor,
 			$10, $11, $12, $13,
 			$14, $15, $16, $17,
 			$18, $19, $20, $21, $22, $23,
-			$24, $25, $26, $27, $28, $29, $30, $31, $32, $33, $34, $35, $36, $37, $38, $39, $40, $41, $42, $43, $44, $45
+			$24, $25, $26, $27, $28, $29, $30, $31, $32, $33, $34, $35, $36, $37, $38, $39, $40, $41, $42, $43, $44, $45, $46
 		)
 		ON CONFLICT (request_id, api_key_id) DO NOTHING
 		RETURNING id, created_at
@@ -797,6 +799,7 @@ func buildUsageLogBatchInsertQuery(keys []string, preparedByKey map[string]usage
 			model_mapping_chain,
 			billing_tier,
 			billing_mode,
+			account_stats_cost,
 			created_at
 		) AS (VALUES `)
 
@@ -873,6 +876,7 @@ func buildUsageLogBatchInsertQuery(keys []string, preparedByKey map[string]usage
 				model_mapping_chain,
 				billing_tier,
 				billing_mode,
+				account_stats_cost,
 				created_at
 			)
 			SELECT
@@ -920,6 +924,7 @@ func buildUsageLogBatchInsertQuery(keys []string, preparedByKey map[string]usage
 				model_mapping_chain,
 				billing_tier,
 				billing_mode,
+				account_stats_cost,
 				created_at
 			FROM input
 			ON CONFLICT (request_id, api_key_id) DO NOTHING
@@ -1007,10 +1012,11 @@ func buildUsageLogBestEffortInsertQuery(preparedList []usageLogInsertPrepared) (
 			model_mapping_chain,
 			billing_tier,
 			billing_mode,
+			account_stats_cost,
 			created_at
 		) AS (VALUES `)
 
-	args := make([]any, 0, len(preparedList)*45)
+	args := make([]any, 0, len(preparedList)*46)
 	argPos := 1
 	for idx, prepared := range preparedList {
 		if idx > 0 {
@@ -1080,6 +1086,7 @@ func buildUsageLogBestEffortInsertQuery(preparedList []usageLogInsertPrepared) (
 			model_mapping_chain,
 			billing_tier,
 			billing_mode,
+			account_stats_cost,
 			created_at
 		)
 		SELECT
@@ -1127,6 +1134,7 @@ func buildUsageLogBestEffortInsertQuery(preparedList []usageLogInsertPrepared) (
 			model_mapping_chain,
 			billing_tier,
 			billing_mode,
+			account_stats_cost,
 			created_at
 		FROM input
 		ON CONFLICT (request_id, api_key_id) DO NOTHING
@@ -1182,6 +1190,7 @@ func execUsageLogInsertNoResult(ctx context.Context, sqlq sqlExecutor, prepared
 			model_mapping_chain,
 			billing_tier,
 			billing_mode,
+			account_stats_cost,
 			created_at
 		) VALUES (
 			$1, $2, $3, $4, $5, $6, $7,
@@ -1189,7 +1198,7 @@ func execUsageLogInsertNoResult(ctx context.Context, sqlq sqlExecutor, prepared
 			$10, $11, $12, $13,
 			$14, $15, $16, $17,
 			$18, $19, $20, $21, $22, $23,
-			$24, $25, $26, $27, $28, $29, $30, $31, $32, $33, $34, $35, $36, $37, $38, $39, $40, $41, $42, $43, $44, $45
+			$24, $25, $26, $27, $28, $29, $30, $31, $32, $33, $34, $35, $36, $37, $38, $39, $40, $41, $42, $43, $44, $45, $46
 		)
 		ON CONFLICT (request_id, api_key_id) DO NOTHING
 	`, prepared.args...)
@@ -1285,6 +1294,7 @@ func prepareUsageLogInsert(log *service.UsageLog) usageLogInsertPrepared {
 			modelMappingChain,
 			billingTier,
 			billingMode,
+			log.AccountStatsCost, // account_stats_cost
 			createdAt,
 		},
 	}
@@ -1959,7 +1969,7 @@ func (r *usageLogRepository) GetAccountTodayStats(ctx context.Context, accountID
 		SELECT
 			COUNT(*) as requests,
 			COALESCE(SUM(input_tokens + output_tokens + cache_creation_tokens + cache_read_tokens), 0) as tokens,
-			COALESCE(SUM(total_cost * COALESCE(account_rate_multiplier, 1)), 0) as cost,
+			COALESCE(SUM(COALESCE(account_stats_cost, total_cost) * COALESCE(account_rate_multiplier, 1)), 0) as cost,
 			COALESCE(SUM(total_cost), 0) as standard_cost,
 			COALESCE(SUM(actual_cost), 0) as user_cost
 		FROM usage_logs
@@ -1989,7 +1999,7 @@ func (r *usageLogRepository) GetAccountWindowStats(ctx context.Context, accountI
 		SELECT
 			COUNT(*) as requests,
 			COALESCE(SUM(input_tokens + output_tokens + cache_creation_tokens + cache_read_tokens), 0) as tokens,
-			COALESCE(SUM(total_cost * COALESCE(account_rate_multiplier, 1)), 0) as cost,
+			COALESCE(SUM(COALESCE(account_stats_cost, total_cost) * COALESCE(account_rate_multiplier, 1)), 0) as cost,
 			COALESCE(SUM(total_cost), 0) as standard_cost,
 			COALESCE(SUM(actual_cost), 0) as user_cost
 		FROM usage_logs
@@ -2026,7 +2036,7 @@ func (r *usageLogRepository) GetAccountWindowStatsBatch(ctx context.Context, acc
 			account_id,
 			COUNT(*) as requests,
 			COALESCE(SUM(input_tokens + output_tokens + cache_creation_tokens + cache_read_tokens), 0) as tokens,
-			COALESCE(SUM(total_cost * COALESCE(account_rate_multiplier, 1)), 0) as cost,
+			COALESCE(SUM(COALESCE(account_stats_cost, total_cost) * COALESCE(account_rate_multiplier, 1)), 0) as cost,
 			COALESCE(SUM(total_cost), 0) as standard_cost,
 			COALESCE(SUM(actual_cost), 0) as user_cost
 		FROM usage_logs
@@ -2990,7 +3000,7 @@ func (r *usageLogRepository) getModelStatsWithFiltersBySource(ctx context.Contex
 	actualCostExpr := "COALESCE(SUM(actual_cost), 0) as actual_cost"
 	// 当仅按 account_id 聚合时，实际费用使用账号倍率（total_cost * account_rate_multiplier）。
 	if accountID > 0 && userID == 0 && apiKeyID == 0 {
-		actualCostExpr = "COALESCE(SUM(total_cost * COALESCE(account_rate_multiplier, 1)), 0) as actual_cost"
+		actualCostExpr = "COALESCE(SUM(COALESCE(account_stats_cost, total_cost) * COALESCE(account_rate_multiplier, 1)), 0) as actual_cost"
 	}
 	modelExpr := resolveModelDimensionExpression(source)
 
@@ -3358,7 +3368,7 @@ func (r *usageLogRepository) GetStatsWithFilters(ctx context.Context, filters Us
 			COALESCE(SUM(cache_creation_tokens + cache_read_tokens), 0) as total_cache_tokens,
 			COALESCE(SUM(total_cost), 0) as total_cost,
 			COALESCE(SUM(actual_cost), 0) as total_actual_cost,
-			COALESCE(SUM(total_cost * COALESCE(account_rate_multiplier, 1)), 0) as total_account_cost,
+			COALESCE(SUM(COALESCE(account_stats_cost, total_cost) * COALESCE(account_rate_multiplier, 1)), 0) as total_account_cost,
 			COALESCE(AVG(duration_ms), 0) as avg_duration_ms
 		FROM usage_logs
 		%s
@@ -3433,7 +3443,7 @@ type EndpointStat = usagestats.EndpointStat
 func (r *usageLogRepository) getEndpointStatsByColumnWithFilters(ctx context.Context, endpointColumn string, startTime, endTime time.Time, userID, apiKeyID, accountID, groupID int64, model string, requestType *int16, stream *bool, billingType *int8) (results []EndpointStat, err error) {
 	actualCostExpr := "COALESCE(SUM(actual_cost), 0) as actual_cost"
 	if accountID > 0 && userID == 0 && apiKeyID == 0 {
-		actualCostExpr = "COALESCE(SUM(total_cost * COALESCE(account_rate_multiplier, 1)), 0) as actual_cost"
+		actualCostExpr = "COALESCE(SUM(COALESCE(account_stats_cost, total_cost) * COALESCE(account_rate_multiplier, 1)), 0) as actual_cost"
 	}
 
 	query := fmt.Sprintf(`
@@ -3500,7 +3510,7 @@ func (r *usageLogRepository) getEndpointStatsByColumnWithFilters(ctx context.Con
 func (r *usageLogRepository) getEndpointPathStatsWithFilters(ctx context.Context, startTime, endTime time.Time, userID, apiKeyID, accountID, groupID int64, model string, requestType *int16, stream *bool, billingType *int8) (results []EndpointStat, err error) {
 	actualCostExpr := "COALESCE(SUM(actual_cost), 0) as actual_cost"
 	if accountID > 0 && userID == 0 && apiKeyID == 0 {
-		actualCostExpr = "COALESCE(SUM(total_cost * COALESCE(account_rate_multiplier, 1)), 0) as actual_cost"
+		actualCostExpr = "COALESCE(SUM(COALESCE(account_stats_cost, total_cost) * COALESCE(account_rate_multiplier, 1)), 0) as actual_cost"
 	}
 
 	query := fmt.Sprintf(`
@@ -3591,7 +3601,7 @@ func (r *usageLogRepository) GetAccountUsageStats(ctx context.Context, accountID
 			COUNT(*) as requests,
 			COALESCE(SUM(input_tokens + output_tokens + cache_creation_tokens + cache_read_tokens), 0) as tokens,
 			COALESCE(SUM(total_cost), 0) as cost,
-			COALESCE(SUM(total_cost * COALESCE(account_rate_multiplier, 1)), 0) as actual_cost,
+			COALESCE(SUM(COALESCE(account_stats_cost, total_cost) * COALESCE(account_rate_multiplier, 1)), 0) as actual_cost,
 			COALESCE(SUM(actual_cost), 0) as user_cost
 		FROM usage_logs
 		WHERE account_id = $1 AND created_at >= $2 AND created_at < $3
@@ -4069,6 +4079,7 @@ func scanUsageLog(scanner interface{ Scan(...any) error }) (*service.UsageLog, e
 		modelMappingChain     sql.NullString
 		billingTier           sql.NullString
 		billingMode           sql.NullString
+		accountStatsCost      sql.NullFloat64
 		createdAt             time.Time
 	)
 
@@ -4118,6 +4129,7 @@ func scanUsageLog(scanner interface{ Scan(...any) error }) (*service.UsageLog, e
 		&modelMappingChain,
 		&billingTier,
 		&billingMode,
+		&accountStatsCost,
 		&createdAt,
 	); err != nil {
 		return nil, err
@@ -4214,6 +4226,9 @@ func scanUsageLog(scanner interface{ Scan(...any) error }) (*service.UsageLog, e
 	if billingMode.Valid {
 		log.BillingMode = &billingMode.String
 	}
+	if accountStatsCost.Valid {
+		log.AccountStatsCost = &accountStatsCost.Float64
+	}
 
 	return log, nil
 }