fix(backups): off-box LastRun is an RFC3339 string — 500'd the backups page

Found during the D0 click-through: OffboxTarget.LastRun persists as an
RFC3339 string (settings.json), but backups.html passed it to timeAgo
(expects time.Time), so GET /backups returned 500 on any node where an
off-box backup had ever run. Pre-existing since v0.93.0 (NAS Part B),
unrelated to the re-skin. New timeAgoStr funcmap helper parses the
string (falls back to the raw value); also v2-token fix for the offbox
error hint (var(--danger) fallback hex) and the dead stat-running/
stat-stopped classes on the offbox status card.

controller/internal/web/templates/backups.html

@@ -123,9 +123,9 @@
 <div class="card" style="margin-bottom:1.5rem">
     {{if .Offbox}}
     <div class="stats-grid backup-page-cards">
-        <div class="stat-card {{if eq .Offbox.LastStatus "ok"}}stat-running{{else if eq .Offbox.LastStatus "error"}}stat-stopped{{end}}">
+        <div class="stat-card {{if eq .Offbox.LastStatus "error"}}stat-warn{{end}}">
             <div class="stat-value" style="font-size:1.15rem">{{if eq .Offbox.LastStatus "ok"}}&#10003; Rendben{{else if eq .Offbox.LastStatus "error"}}&#10007; Hiba{{else if eq .Offbox.LastStatus "running"}}Fut…{{else}}–{{end}}</div>
-            <div class="stat-label">Utolsó NAS-mentés{{if .Offbox.LastRun}}<br><span class="relative-time">{{timeAgo .Offbox.LastRun}}</span>{{end}}</div>
+            <div class="stat-label">Utolsó NAS-mentés{{if .Offbox.LastRun}}<br><span class="relative-time">{{timeAgoStr .Offbox.LastRun}}</span>{{end}}</div>
         </div>
         <div class="stat-card">
             <div class="stat-value" style="font-size:1.15rem">{{if .Offbox.RepoSizeHuman}}{{.Offbox.RepoSizeHuman}}{{else}}–{{end}}</div>
@@ -136,7 +136,7 @@
             <div class="stat-label">{{if .Offbox.Enabled}}{{.Offbox.RepoPath}}{{else}}A NAS-mentés ki van kapcsolva{{end}}</div>
         </div>
     </div>
-    {{if .Offbox.LastError}}<p class="form-hint" style="color:var(--danger,#c0392b)">Utolsó hiba: {{.Offbox.LastError}}</p>{{end}}
+    {{if .Offbox.LastError}}<p class="form-hint" style="color:var(--crit)">Utolsó hiba: {{.Offbox.LastError}}</p>{{end}}
     {{if .OffboxConfigured}}
     <div class="schedule-actions" style="margin-top:1rem">
         <form method="POST" action="/backup/offbox/run" style="display:inline">{{.CSRFField}}