fix: USB badge detection for bind-mounted drives + graceful Tier2 backup on disconnected destinations

- IsUSBDevice/diskModel: strip findmnt bind-mount suffix [/subdir] before
  parsing device path (fixes USB badge not showing for attach-wizard drives)
- crossdrive.go: skip disconnected src/dest drives with WARN log instead of
  returning error (prevents noisy error status in settings.json)
- handlers.go: detect Tier2 destination disconnection, set yellow status dot
  instead of red, skip ValidateDestination for disconnected paths
- backups.html: new template branch showing "Cél meghajtó leválasztva" badge
  with grayed-out info and hidden "Futtatás most" button

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

controller/internal/web/templates/backups.html

@@ -295,7 +295,18 @@
                 <!-- Tier 2: Cross-drive backup (opt-in, different device) -->
                 <div class="backup-layer-row">
                     <span class="tier-label">2. mentés</span>
-                    {{if .Tier2Configured}}
+                    {{if and .Tier2Configured .Tier2DestDisconnected}}
+                        <span class="layer-method" style="opacity:.6">rsync</span>
+                        <span class="layer-dest" style="opacity:.6">→ {{.Tier2Dest}}</span>
+                        <span class="badge badge-warn" style="font-size:.7rem">Cél meghajtó leválasztva</span>
+                        {{if .Tier2LastRun}}
+                        <span class="layer-last" style="opacity:.6">Utolsó: {{.Tier2LastRun}}</span>
+                        {{end}}
+                        <span class="tier-contents" style="opacity:.6">{{.BackupContents}}</span>
+                        <div class="layer-actions">
+                            <a href="/stacks/{{.StackName}}/deploy" class="btn btn-xs btn-outline">Beállítás</a>
+                        </div>
+                    {{else if .Tier2Configured}}
                         <span class="layer-method">rsync</span>
                         <span class="layer-dest">→ {{.Tier2Dest}}</span>
                         <span class="layer-schedule">{{.Tier2Schedule}}</span>