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/status.go

@@ -1,10 +1,67 @@
 package handlers
 
 import (
+	"log"
 	"net/http"
 	"time"
+
+	"github.com/kjannette/koin-ping/backend-go/internal/models"
 )
 
+// StatusHandler handles the system status endpoint.
+type StatusHandler struct {
+	checkpoints *models.CheckpointModel
+}
+
+// NewStatusHandler creates a new StatusHandler.
+func NewStatusHandler(checkpoints *models.CheckpointModel) *StatusHandler {
+	return &StatusHandler{checkpoints: checkpoints}
+}
+
+// GetStatus returns real-time system status derived from checkpoint data.
+func (h *StatusHandler) GetStatus(w http.ResponseWriter, r *http.Request) {
+	block, checkedAt, err := h.checkpoints.GetLatestBlock(r.Context())
+	if err != nil {
+		log.Printf("Error querying latest block: %v", err)
+		writeError(w, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to get system status")
+
+		return
+	}
+
+	latestBlock := 0
+	lag := 0
+	status := "starting"
+
+	if checkedAt != nil {
+		lag = int(time.Since(*checkedAt).Seconds())
+		if lag > 600 { //nolint:mnd
+			status = "idle"
+		} else {
+			status = "active"
+		}
+	}
+
+	if block != nil {
+		latestBlock = *block
+	}
+
+	writeJSON(w, http.StatusOK, map[string]interface{}{
+		"status":        status,
+		"latestBlock":   latestBlock,
+		"lag":           lag,
+		"lastCheckedAt": checkedAtStr(checkedAt),
+		"timestamp":     time.Now().UTC().Format(time.RFC3339),
+	})
+}
+
+func checkedAtStr(t *time.Time) string {
+	if t == nil {
+		return ""
+	}
+
+	return t.UTC().Format(time.RFC3339)
+}
+
 func HealthCheck(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, map[string]interface{}{
 		"status":    "ok",
@@ -12,12 +69,3 @@ func HealthCheck(w http.ResponseWriter, r *http.Request) {
 		"service":   "koin-ping-backend",
 	})
 }
-
-func SystemStatus(w http.ResponseWriter, r *http.Request) {
-	writeJSON(w, http.StatusOK, map[string]interface{}{
-		"latestBlock": 0,
-		"lag":         0,
-		"status":      "healthy",
-		"timestamp":   time.Now().UTC().Format(time.RFC3339),
-	})
-}