Alert when an integration or DNS provider fails repeatedly

The Diagnostic Log already records every outbound call's success or
failure, but nothing acted on it — you'd only notice an integration
was down by happening to open its page. Adds a per-source consecutive-
failure counter (in-memory, reset on restart, same durability tier as
the diag log's own ring buffer) hooked into recordDiagEntry: crossing
the configurable threshold (default 3) sends one "down" notification
on every configured channel, and a "recovered" notification fires once
it succeeds again — no repeat spam while it stays down. New
"Integration/DNS provider failing repeatedly" toggle and threshold
field under Settings -> Notifications.

Verified end-to-end against an isolated scratch database with a real
local HTTP server standing in for the webhook channel: 5 consecutive
failures produced exactly one "Down" notification (at the 3rd
failure, correctly naming "3 calls"), a subsequent success produced
exactly one "Recovered" notification, and two more failures on a
fresh streak triggered nothing (below threshold) — confirmed the real
dev database's mtime was untouched throughout.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

server/src/services/integrationHealthMonitor.ts

@@ -0,0 +1,38 @@
+import { getSettings } from "./settingsStore.js";
+import { notifyIntegrationDown, notifyIntegrationRecovered } from "./notify.js";
+
+interface SourceHealth {
+  consecutiveFailures: number;
+  /** True once a "down" notification has been sent for the current failure streak, so it isn't repeated on every subsequent failure. */
+  alerted: boolean;
+}
+
+/**
+ * In-memory only (like the diag log's own ring buffer — resets on restart,
+ * which is fine since this tracks a live streak, not history). Keyed by diag
+ * log "source" (e.g. "proxmox", "cloudflare") — the same granularity the
+ * Diagnostic Log itself filters by, so a homelab running two integrations of
+ * the same type shares one health streak between them.
+ */
+const health = new Map<string, SourceHealth>();
+
+/** Called after every diagnostic-log entry is recorded, to track consecutive failures per source and alert on threshold-cross / recovery. */
+export async function trackIntegrationHealth(source: string, ok: boolean): Promise<void> {
+  const state = health.get(source) ?? { consecutiveFailures: 0, alerted: false };
+
+  if (ok) {
+    if (state.alerted) {
+      await notifyIntegrationRecovered(source);
+    }
+    health.set(source, { consecutiveFailures: 0, alerted: false });
+    return;
+  }
+
+  state.consecutiveFailures += 1;
+  const { notifications } = await getSettings();
+  if (notifications.integrationFailureAlerts && !state.alerted && state.consecutiveFailures >= notifications.integrationFailureThreshold) {
+    state.alerted = true;
+    await notifyIntegrationDown(source, state.consecutiveFailures);
+  }
+  health.set(source, state);
+}