feat: add Web UI for notification config (feishu + email)

- New config/notify_store.go: persistent notification config (notify.json)
- New API: GET/PUT /api/notify/config, POST /api/notify/test-feishu, POST /api/notify/test-email
- New Vue page: NotifyConfig.vue with feishu webhook and SMTP settings
- Updated cron/init to read from persistent store instead of env vars
- Password masked as ******** in API responses, preserved on updates

backend/config/config.go

@@ -72,6 +72,12 @@ func InitStore(cfg *Config) {
 	log.Println("Cert store initialized successfully")
 }
 
+// InitAll initializes all stores
+func InitAll(cfg *Config) {
+	InitStore(cfg)
+	InitNotifyStore(cfg)
+}
+
 // Load reads certificates from JSON file into memory
 func (s *CertStore) Load() error {
 	s.mu.Lock()