audit: fix issues #1-#9 (mock data, notifier interface, retry/timeout, digest scheduling, real status, RPC retry, dedup, address edit UI)

- #1: remove mock alert events that poisoned production responses
- #2: add Notifier interface + Send implementations for all channels
- #3/#4: notification goroutines now carry a 30s context timeout and retry up to 3x with exponential backoff
- #5: schedule email digest in poller via DIGEST_INTERVAL_HOURS (default 24h)
- #6: SystemStatus queries real checkpoint data; returns starting/active/idle with latestBlock and lag
- #7: Ethereum RPC client retries on network errors, 429, and 5xx with 1s/2s backoff
- #8: alert_events dedup index + ON CONFLICT DO NOTHING to prevent duplicate events on poller restart
- #9: PATCH /v1/addresses/{id} for label editing; frontend address list gains inline edit and remove buttons

backend-go/cmd/api/main.go

@@ -47,6 +47,7 @@ func main() {
 	addressModel := models.NewAddressModel(pool)
 	alertRuleModel := models.NewAlertRuleModel(pool)
 	alertEventModel := models.NewAlertEventModel(pool)
+	checkpointModel := models.NewCheckpointModel(pool)
 	notifConfigModel := models.NewNotificationConfigModel(pool)
 
 	emailDigestSvc := services.NewEmailDigestService(
@@ -58,13 +59,14 @@ func main() {
 	alertEventHandler := handlers.NewAlertEventHandler(alertEventModel)
 	notifConfigHandler := handlers.NewNotificationConfigHandler(notifConfigModel, cfg)
 	emailDigestHandler := handlers.NewEmailDigestHandler(emailDigestSvc, notifConfigModel)
+	statusHandler := handlers.NewStatusHandler(checkpointModel)
 
 	mux := http.NewServeMux()
 	b := cfg.APIBasePath // e.g. "/v1"
 
 	// Public routes
 	mux.HandleFunc("GET "+b+"/health", handlers.HealthCheck)
-	mux.HandleFunc("GET "+b+"/status", handlers.SystemStatus)
+	mux.HandleFunc("GET "+b+"/status", statusHandler.GetStatus)
 
 	// Authenticated routes — addresses
 	mux.Handle("POST "+b+"/addresses",
@@ -73,6 +75,8 @@ func main() {
 		middleware.Authenticate(http.HandlerFunc(addressHandler.List)))
 	mux.Handle("DELETE "+b+"/addresses/{addressId}",
 		middleware.Authenticate(http.HandlerFunc(addressHandler.Remove)))
+	mux.Handle("PATCH "+b+"/addresses/{addressId}",
+		middleware.Authenticate(http.HandlerFunc(addressHandler.UpdateLabel)))
 
 	// Authenticated routes for alert rules
 	mux.Handle("POST "+b+"/addresses/{addressId}/alerts",