feat: 图片生成计费功能

- 新增 Group 图片价格配置（image_price_1k/2k/4k）
- BillingService 新增 CalculateImageCost 方法
- AntigravityGatewayService 支持识别图片生成模型并按次计费
- UsageLog 新增 image_count 和 image_size 字段
- 前端分组管理支持配置图片价格（antigravity 和 gemini 平台）
- 图片计费复用通用计费能力（余额检查、扣费、倍率、订阅限额）

backend/internal/repository/api_key_repo.go

@@ -321,6 +321,9 @@ func groupEntityToService(g *dbent.Group) *service.Group {
 		DailyLimitUSD:       g.DailyLimitUsd,
 		WeeklyLimitUSD:      g.WeeklyLimitUsd,
 		MonthlyLimitUSD:     g.MonthlyLimitUsd,
+		ImagePrice1K:        g.ImagePrice1k,
+		ImagePrice2K:        g.ImagePrice2k,
+		ImagePrice4K:        g.ImagePrice4k,
 		DefaultValidityDays: g.DefaultValidityDays,
 		CreatedAt:           g.CreatedAt,
 		UpdatedAt:           g.UpdatedAt,

backend/internal/repository/group_repo.go

@@ -43,6 +43,9 @@ func (r *groupRepository) Create(ctx context.Context, groupIn *service.Group) er
 		SetNillableDailyLimitUsd(groupIn.DailyLimitUSD).
 		SetNillableWeeklyLimitUsd(groupIn.WeeklyLimitUSD).
 		SetNillableMonthlyLimitUsd(groupIn.MonthlyLimitUSD).
+		SetNillableImagePrice1k(groupIn.ImagePrice1K).
+		SetNillableImagePrice2k(groupIn.ImagePrice2K).
+		SetNillableImagePrice4k(groupIn.ImagePrice4K).
 		SetDefaultValidityDays(groupIn.DefaultValidityDays)
 
 	created, err := builder.Save(ctx)
@@ -80,6 +83,9 @@ func (r *groupRepository) Update(ctx context.Context, groupIn *service.Group) er
 		SetNillableDailyLimitUsd(groupIn.DailyLimitUSD).
 		SetNillableWeeklyLimitUsd(groupIn.WeeklyLimitUSD).
 		SetNillableMonthlyLimitUsd(groupIn.MonthlyLimitUSD).
+		SetNillableImagePrice1k(groupIn.ImagePrice1K).
+		SetNillableImagePrice2k(groupIn.ImagePrice2K).
+		SetNillableImagePrice4k(groupIn.ImagePrice4K).
 		SetDefaultValidityDays(groupIn.DefaultValidityDays).
 		Save(ctx)
 	if err != nil {

backend/internal/repository/usage_log_repo.go

@@ -22,7 +22,7 @@ import (
 	"github.com/lib/pq"
 )
 
-const usageLogSelectColumns = "id, user_id, api_key_id, account_id, request_id, model, group_id, subscription_id, input_tokens, output_tokens, cache_creation_tokens, cache_read_tokens, cache_creation_5m_tokens, cache_creation_1h_tokens, input_cost, output_cost, cache_creation_cost, cache_read_cost, total_cost, actual_cost, rate_multiplier, billing_type, stream, duration_ms, first_token_ms, created_at"
+const usageLogSelectColumns = "id, user_id, api_key_id, account_id, request_id, model, group_id, subscription_id, input_tokens, output_tokens, cache_creation_tokens, cache_read_tokens, cache_creation_5m_tokens, cache_creation_1h_tokens, input_cost, output_cost, cache_creation_cost, cache_read_cost, total_cost, actual_cost, rate_multiplier, billing_type, stream, duration_ms, first_token_ms, image_count, image_size, created_at"
 
 type usageLogRepository struct {
 	client *dbent.Client
@@ -109,6 +109,8 @@ func (r *usageLogRepository) Create(ctx context.Context, log *service.UsageLog)
 			stream,
 			duration_ms,
 			first_token_ms,
+			image_count,
+			image_size,
 			created_at
 		) VALUES (
 			$1, $2, $3, $4, $5,
@@ -116,7 +118,8 @@ func (r *usageLogRepository) Create(ctx context.Context, log *service.UsageLog)
 			$8, $9, $10, $11,
 			$12, $13,
 			$14, $15, $16, $17, $18, $19,
-			$20, $21, $22, $23, $24, $25
+			$20, $21, $22, $23, $24,
+			$25, $26, $27
 		)
 		ON CONFLICT (request_id, api_key_id) DO NOTHING
 		RETURNING id, created_at
@@ -126,6 +129,7 @@ func (r *usageLogRepository) Create(ctx context.Context, log *service.UsageLog)
 	subscriptionID := nullInt64(log.SubscriptionID)
 	duration := nullInt(log.DurationMs)
 	firstToken := nullInt(log.FirstTokenMs)
+	imageSize := nullString(log.ImageSize)
 
 	var requestIDArg any
 	if requestID != "" {
@@ -157,6 +161,8 @@ func (r *usageLogRepository) Create(ctx context.Context, log *service.UsageLog)
 		log.Stream,
 		duration,
 		firstToken,
+		log.ImageCount,
+		imageSize,
 		createdAt,
 	}
 	if err := scanSingleRow(ctx, sqlq, query, args, &log.ID, &log.CreatedAt); err != nil {
@@ -1789,6 +1795,8 @@ func scanUsageLog(scanner interface{ Scan(...any) error }) (*service.UsageLog, e
 		stream              bool
 		durationMs          sql.NullInt64
 		firstTokenMs        sql.NullInt64
+		imageCount          int
+		imageSize           sql.NullString
 		createdAt           time.Time
 	)
 
@@ -1818,6 +1826,8 @@ func scanUsageLog(scanner interface{ Scan(...any) error }) (*service.UsageLog, e
 		&stream,
 		&durationMs,
 		&firstTokenMs,
+		&imageCount,
+		&imageSize,
 		&createdAt,
 	); err != nil {
 		return nil, err
@@ -1844,6 +1854,7 @@ func scanUsageLog(scanner interface{ Scan(...any) error }) (*service.UsageLog, e
 		RateMultiplier:        rateMultiplier,
 		BillingType:           int8(billingType),
 		Stream:                stream,
+		ImageCount:            imageCount,
 		CreatedAt:             createdAt,
 	}
 
@@ -1866,6 +1877,9 @@ func scanUsageLog(scanner interface{ Scan(...any) error }) (*service.UsageLog, e
 		value := int(firstTokenMs.Int64)
 		log.FirstTokenMs = &value
 	}
+	if imageSize.Valid {
+		log.ImageSize = &imageSize.String
+	}
 
 	return log, nil
 }
@@ -1938,6 +1952,13 @@ func nullInt(v *int) sql.NullInt64 {
 	return sql.NullInt64{Int64: int64(*v), Valid: true}
 }
 
+func nullString(v *string) sql.NullString {
+	if v == nil || *v == "" {
+		return sql.NullString{}
+	}
+	return sql.NullString{String: *v, Valid: true}
+}
+
 func setToSlice(set map[int64]struct{}) []int64 {
 	out := make([]int64, 0, len(set))
 	for id := range set {