feat: auto-resume queue toggle + already-downloaded VOD indicator

Two real UX wins.

1. Auto-resume queue on startup. New checkbox in Settings -> Download
   ("Queue beim Start automatisch fortsetzen"). When enabled and the
   persisted queue has pending items, processQueue() fires ~5 seconds
   after did-finish-load — long enough for the user to see the queue
   and pause if they did not actually want this. Default off so the
   existing behaviour (explicit Start click) is preserved on upgrade.
   The Settings auto-save fingerprint includes the new flag and
   syncSettingsFormFromConfig restores it. Tooltip explains the
   timing on hover.

2. Already-downloaded indicator on VOD cards. Config gains
   downloaded_vod_ids: string[] (bounded to 4096 latest entries).
   Every successful queue-item download appends its parsed VOD ID
   (or every component ID for merge groups). On the VOD grid each
   card whose vod.id is in the set gets a small green checkmark
   badge in the top-right plus a slightly dimmed thumbnail, with a
   localized "Already downloaded" / "Bereits heruntergeladen"
   tooltip. The lookup builds a Set once per render so it stays
   O(1) per card. The renderer refreshes its local config copy on
   every "newly completed" queue update so the badge appears live
   without waiting for a settings save.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/index.html

@@ -493,6 +493,10 @@
                                 <input type="checkbox" id="persistQueueToggle" checked>
                                 <span id="persistQueueLabel">Queue zwischen App-Starts speichern</span>
                             </label>
+                            <label style="display:flex; align-items:center; gap:8px; margin-top: 8px;">
+                                <input type="checkbox" id="autoResumeQueueToggle">
+                                <span id="autoResumeQueueLabel">Queue beim Start automatisch fortsetzen</span>
+                            </label>
                         </div>
                         <div class="form-group">
                             <label id="metadataCacheMinutesLabel">Metadata-Cache (Minuten)</label>