feat: storage watchdog — USB disconnect detection, auto-stop, safe eject, auto-reconnect (v0.17.0)

New storage watchdog monitors registered storage paths every 5s. On disconnect
(3 consecutive probe failures), auto-stops affected apps, lazy-unmounts stale
VFS entries, fires alerts/notifications/hub report. On reconnect (UUID detected),
auto-remounts via fstab, cleans stale restic locks, offers app restart.

Safe disconnect UI for USB drives: confirmation dialog, stop apps, sync, unmount.
Disconnected state visible across all pages (dashboard, settings, backups, monitoring)
with hatched red bars and badges. Backup guards skip disconnected drives.

22 files changed (1 new: monitor/watchdog.go), ~1500 lines added.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

controller/internal/web/templates/backups.html

@@ -38,6 +38,15 @@
                 </div>
             </div>
             {{range $.StorageBars}}
+            {{if .Disconnected}}
+            <div class="storage-item storage-disconnected">
+                <div class="storage-header">
+                    <span class="storage-label">{{.Label}}</span>
+                    <span class="storage-value badge-error" style="font-size:.75rem">Leválasztva</span>
+                </div>
+                <div class="system-bar"><div class="system-bar-disconnected"></div></div>
+            </div>
+            {{else}}
             <div class="storage-item">
                 <div class="storage-header">
                     <span class="storage-label">{{.Label}}</span>
@@ -49,6 +58,7 @@
             </div>
             {{end}}
             {{end}}
+            {{end}}
         </div>
         <div class="storage-stats">
             {{if .Backup.RepoStats}}
@@ -253,7 +263,9 @@
             <span class="status-dot status-{{.Status}}" title="{{.StatusText}}"></span>
             <span class="app-backup-row-name">{{.DisplayName}}</span>
             <div class="app-backup-row-meta">
-                {{if .HasHDDData}}
+                {{if .DriveDisconnected}}
+                    <span class="badge badge-error" style="font-size:.7rem">Meghajtó leválasztva</span>
+                {{else if .HasHDDData}}
                     {{if .StorageLabel}}<span class="meta-badge meta-badge-storage">{{.StorageLabel}}</span>{{end}}
                     <span class="mono app-backup-size" style="font-size:.8rem">{{.HDDSizeHuman}}</span>
                 {{else}}