Surface Proxmox backup job status, with a daily failure notification

Proxmox already runs vzdump backups, but nothing in the app said
whether they were actually succeeding — a silent backup failure is
one of the more dangerous blind spots a homelab admin can have. Adds
a "Backups" card to the Proxmox page: configured backup job
schedules (storage target, which guests, enabled/disabled) from
GET /cluster/backup, and recent vzdump task history per node from
GET /nodes/{node}/tasks?typefilter=vzdump, with a banner at the top
if the most recent run didn't succeed.

New "Proxmox backup failed" notification toggle under Settings ->
Notifications, on the same daily schedule as the other checks. The
scheduler checks each node's own most-recent vzdump run independently
(not just the single most recent task overall) so one node's healthy
backup can't mask another node's failing one in a multi-node cluster.

Known limitation, documented in the adapter's own header comment:
Proxmox's task list doesn't reliably expose which specific guest
failed within an "all guests" job — only the task's own log text has
that — so this surfaces job- and task-level status rather than
guessing at per-guest outcomes.

Verified against a fake Proxmox server (real self-signed HTTPS, since
the adapter's node:https usage can't be monkey-patched under ESM)
reproducing the documented /cluster/backup and task-list response
shapes: job parsing (all-guests+exclude vs specific-vmids+disabled)
correct, task OK/failure parsing correct, and the critical multi-node
scenario confirmed — one node's failing latest run flagged, the
other's healthy latest run correctly left alone, with exactly one
notification of the right content. This reproduces Proxmox's
documented API shape rather than a live-verified one; flag if the
real cluster's response differs in some way this didn't anticipate.
Confirmed the real dev database's mtime was untouched throughout.

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

server/src/services/settingsStore.ts

@@ -41,7 +41,8 @@ export interface NotificationEvents {
   secretCheck: boolean;
   tailscaleKeyCheck: boolean;
   dockerUpdateCheck: boolean;
-  secretCheckTime: string; // "HH:MM" — shared by the secret-expiry, Tailscale key-expiry, and Docker update checks
+  proxmoxBackupCheck: boolean;
+  secretCheckTime: string; // "HH:MM" — shared by the secret-expiry, Tailscale key-expiry, Docker update, and Proxmox backup checks
   timezone: string;
   integrationFailureAlerts: boolean;
   /** Consecutive failed calls (from the Diagnostic Log) before an integration/DNS provider is considered down. */
@@ -93,6 +94,7 @@ const DEFAULTS: AppSettings = {
     secretCheck: true,
     tailscaleKeyCheck: true,
     dockerUpdateCheck: true,
+    proxmoxBackupCheck: true,
     secretCheckTime: "08:00",
     timezone: "UTC",
     integrationFailureAlerts: true,