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/internal/handlers/address.go

@@ -92,6 +92,44 @@ func (h *AddressHandler) List(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, addresses)
 }
 
+// UpdateLabel handles PATCH requests to update an address label.
+func (h *AddressHandler) UpdateLabel(w http.ResponseWriter, r *http.Request) {
+	userID := middleware.GetUserID(r.Context())
+	addressID, ok := parseIntParam(r.PathValue("addressId"))
+	if !ok {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid address ID")
+
+		return
+	}
+
+	var body struct {
+		Label *string `json:"label"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
+
+		return
+	}
+
+	log.Printf("User %s updating label for address ID: %d", userID, addressID)
+
+	addr, err := h.addresses.UpdateLabel(r.Context(), addressID, userID, body.Label)
+	if err != nil {
+		log.Printf("Error updating address label: %v", err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to update address")
+
+		return
+	}
+
+	if addr == nil {
+		writeError(w, http.StatusNotFound, "NOT_FOUND", "Address not found")
+
+		return
+	}
+
+	writeJSON(w, http.StatusOK, addr)
+}
+
 // Remove handles DELETE requests to remove a tracked address.
 func (h *AddressHandler) Remove(w http.ResponseWriter, r *http.Request) {
 	userID := middleware.GetUserID(r.Context())