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/service/ops_system_log_sink_test.go

@@ -183,6 +183,15 @@ func TestOpsSystemLogSink_StartStopAndFlushSuccess(t *testing.T) {
 	if strings.TrimSpace(item.Message) == "" {
 		t.Fatalf("message should not be empty")
 	}
+	// writtenCount is incremented after BatchInsertSystemLogsFn returns,
+	// so poll briefly to avoid a race between the done signal and the atomic add.
+	deadline := time.Now().Add(time.Second)
+	for time.Now().Before(deadline) {
+		if sink.Health().WrittenCount > 0 {
+			break
+		}
+		time.Sleep(time.Millisecond)
+	}
 	health := sink.Health()
 	if health.WrittenCount == 0 {
 		t.Fatalf("written_count should be >0")