Replace Gorush with direct APNs/FCM integration

- Add direct APNs client using sideshow/apns2 for iOS push
- Add direct FCM client using legacy HTTP API for Android push
- Remove Gorush dependency (no external push server needed)
- Update all services/handlers to use new push.Client
- Update config for APNS_PRODUCTION flag

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

internal/admin/handlers/notification_handler.go

@@ -19,11 +19,11 @@ import (
 type AdminNotificationHandler struct {
 	db           *gorm.DB
 	emailService *services.EmailService
-	pushClient   *push.GorushClient
+	pushClient   *push.Client
 }
 
 // NewAdminNotificationHandler creates a new admin notification handler
-func NewAdminNotificationHandler(db *gorm.DB, emailService *services.EmailService, pushClient *push.GorushClient) *AdminNotificationHandler {
+func NewAdminNotificationHandler(db *gorm.DB, emailService *services.EmailService, pushClient *push.Client) *AdminNotificationHandler {
 	return &AdminNotificationHandler{
 		db:           db,
 		emailService: emailService,

internal/admin/routes.go

@@ -20,7 +20,7 @@ import (
 // Dependencies holds optional services for admin routes
 type Dependencies struct {
 	EmailService *services.EmailService
-	PushClient   *push.GorushClient
+	PushClient   *push.Client
 }
 
 // SetupRoutes configures all admin routes
@@ -114,7 +114,7 @@ func SetupRoutes(router *gin.Engine, db *gorm.DB, cfg *config.Config, deps *Depe
 
 			// Notification management
 			var emailService *services.EmailService
-			var pushClient *push.GorushClient
+			var pushClient *push.Client
 			if deps != nil {
 				emailService = deps.EmailService
 				pushClient = deps.PushClient