fix: merge 30 general improvements from release branch

Bug fixes:
- Detached context for GetAccountConcurrencyBatch (prevent all-zero on request cancel)
- Filter soft-deleted users in GetByGroupID
- Stripe CSP policy (allow Stripe.js in script-src and frame-src)
- WebSearch API key validation on save
- RECHARGING status in payment result success check
- Windows test fixes (logger Sync deadlock, config path escaping)

Feature enhancements:
- Webhook multi-instance dispatch (extractOutTradeNo + GetWebhookProvider)
- EasyPay mobile H5 payment (device param + PayURL2)
- SSE error propagation in WebSearch emulation
- AccountStatsCost DTO field for admin usage logs
- Plans sort by sort_order instead of created_at
- UsageMapHook for streaming response usage data
- apicompat Instructions field passthrough
- EffectiveLoadFactor for ops concurrency/metrics
- Usage billing RETURNING balance for notify system
- BulkUpdate mixed channel warning with details
- println to slog migration in auth cache
- Wire ProviderSet cleanup
- CI cache-dependency-path optimization

Frontend:
- Refund eligibility check per provider (canRequestRefund)
- Plan sort_order editing
- Dead code cleanup (simulate_claude_max, client_affinity)
- GroupsView platform switch guard
- channels features_config API type
- UsageView account_stats_cost export

backend/internal/pkg/antigravity/stream_transformer.go

@@ -18,6 +18,9 @@ const (
 	BlockTypeFunction
 )
 
+// UsageMapHook is a callback that can modify usage data before it's emitted in SSE events.
+type UsageMapHook func(usageMap map[string]any)
+
 // StreamingProcessor 流式响应处理器
 type StreamingProcessor struct {
 	blockType         BlockType
@@ -30,6 +33,7 @@ type StreamingProcessor struct {
 	originalModel     string
 	webSearchQueries  []string
 	groundingChunks   []GeminiGroundingChunk
+	usageMapHook      UsageMapHook
 
 	// 累计 usage
 	inputTokens       int
@@ -46,6 +50,28 @@ func NewStreamingProcessor(originalModel string) *StreamingProcessor {
 	}
 }
 
+// SetUsageMapHook sets an optional hook that modifies usage maps before they are emitted.
+func (p *StreamingProcessor) SetUsageMapHook(fn UsageMapHook) {
+	p.usageMapHook = fn
+}
+
+func usageToMap(u ClaudeUsage) map[string]any {
+	m := map[string]any{
+		"input_tokens":  u.InputTokens,
+		"output_tokens": u.OutputTokens,
+	}
+	if u.CacheCreationInputTokens > 0 {
+		m["cache_creation_input_tokens"] = u.CacheCreationInputTokens
+	}
+	if u.CacheReadInputTokens > 0 {
+		m["cache_read_input_tokens"] = u.CacheReadInputTokens
+	}
+	if u.ImageOutputTokens > 0 {
+		m["image_output_tokens"] = u.ImageOutputTokens
+	}
+	return m
+}
+
 // ProcessLine 处理 SSE 行，返回 Claude SSE 事件
 func (p *StreamingProcessor) ProcessLine(line string) []byte {
 	line = strings.TrimSpace(line)
@@ -172,6 +198,13 @@ func (p *StreamingProcessor) emitMessageStart(v1Resp *V1InternalResponse) []byte
 		responseID = "msg_" + generateRandomID()
 	}
 
+	var usageValue any = usage
+	if p.usageMapHook != nil {
+		usageMap := usageToMap(usage)
+		p.usageMapHook(usageMap)
+		usageValue = usageMap
+	}
+
 	message := map[string]any{
 		"id":            responseID,
 		"type":          "message",
@@ -180,7 +213,7 @@ func (p *StreamingProcessor) emitMessageStart(v1Resp *V1InternalResponse) []byte
 		"model":         p.originalModel,
 		"stop_reason":   nil,
 		"stop_sequence": nil,
-		"usage":         usage,
+		"usage":         usageValue,
 	}
 
 	event := map[string]any{
@@ -492,13 +525,20 @@ func (p *StreamingProcessor) emitFinish(finishReason string) []byte {
 		ImageOutputTokens:    p.imageOutputTokens,
 	}
 
+	var usageValue any = usage
+	if p.usageMapHook != nil {
+		usageMap := usageToMap(usage)
+		p.usageMapHook(usageMap)
+		usageValue = usageMap
+	}
+
 	deltaEvent := map[string]any{
 		"type": "message_delta",
 		"delta": map[string]any{
 			"stop_reason":   stopReason,
 			"stop_sequence": nil,
 		},
-		"usage": usage,
+		"usage": usageValue,
 	}
 
 	_, _ = result.Write(p.formatSSE("message_delta", deltaEvent))