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/server/routes/payment.go

@@ -26,6 +26,7 @@ func RegisterPaymentRoutes(
 	authenticated.Use(middleware.BackendModeUserGuard(settingService))
 	{
 		authenticated.GET("/config", paymentHandler.GetPaymentConfig)
+		authenticated.GET("/checkout-info", paymentHandler.GetCheckoutInfo)
 		authenticated.GET("/plans", paymentHandler.GetPlans)
 		authenticated.GET("/channels", paymentHandler.GetChannels)
 		authenticated.GET("/limits", paymentHandler.GetLimits)
@@ -33,6 +34,7 @@ func RegisterPaymentRoutes(
 		orders := authenticated.Group("/orders")
 		{
 			orders.POST("", paymentHandler.CreateOrder)
+			orders.POST("/verify", paymentHandler.VerifyOrder)
 			orders.GET("/my", paymentHandler.GetMyOrders)
 			orders.GET("/:id", paymentHandler.GetOrder)
 			orders.POST("/:id/cancel", paymentHandler.CancelOrder)
@@ -52,6 +54,8 @@ func RegisterPaymentRoutes(
 	// --- Webhook endpoints (no auth) ---
 	webhook := v1.Group("/payment/webhook")
 	{
+		// EasyPay sends GET callbacks with query params
+		webhook.GET("/easypay", webhookHandler.EasyPayNotify)
 		webhook.POST("/easypay", webhookHandler.EasyPayNotify)
 		webhook.POST("/alipay", webhookHandler.AlipayNotify)
 		webhook.POST("/wxpay", webhookHandler.WxpayNotify)