feat: auto-vod-download — per-streamer VOD toggle + background poller

Adds the second half of the live-archive flow. AUTO catches a stream
as it happens; VOD catches the recently published archive. Both
together close the gap a Twitch viewer-side archivist cares about.

Streamer list grows a third per-streamer toggle (blue "VOD") next
to AUTO and REC. When enabled, the main-process auto-VOD poller
periodically scans that streamer's VOD list and queues anything
that is (a) within the rolling age window, (b) not already in
downloaded_vod_ids, and (c) not already in the active queue. The
age window keeps freshly-enabled streamers from suddenly dumping
their entire historical backlog into the queue — when a user flips
VOD on, only VODs published in the last N hours (default 24, capped
at 720) get auto-pulled.

Polling cadence is in minutes, not seconds — VOD-listing scans are
heavier than live-status checks and new VODs only appear after a
stream ends, so minute-level lag is fine. Default 15 min, clamped
[5, 360]. Independent timer from the auto-record poller because
their cadences shouldn't be coupled.

UI:
- Streamer item: blue "VOD" pill next to AUTO/REC, identical interaction.
- Settings card "Auto-VOD download": poll interval + max age fields.
- Discord card: optional "Notify when a VOD gets auto-queued" checkbox.

Wires through save-config so toggling triggers restartAutoVodPoller
without a full app restart, and through shutdownCleanup so the
timer is killed on quit.

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

src/index.html

@@ -686,6 +686,21 @@
                                 <input type="checkbox" id="discordNotifyVodCompleteToggle">
                                 <span id="discordNotifyVodCompleteLabel">Bei abgeschlossenem VOD-Download benachrichtigen</span>
                             </label>
+                            <label style="display:flex; align-items:center; gap:8px; margin-top: 8px;">
+                                <input type="checkbox" id="discordNotifyVodAutoQueuedToggle">
+                                <span id="discordNotifyVodAutoQueuedLabel">Bei automatisch eingereihten VODs benachrichtigen</span>
+                            </label>
+                        </div>
+                    </div>
+
+                    <div class="settings-card">
+                        <h3 id="autoVodCardTitle">Auto-VOD-Download</h3>
+                        <p id="autoVodCardIntro" style="color: var(--text-secondary); font-size:13px; margin-bottom:12px; line-height:1.5;">Streamer mit aktiviertem VOD-Toggle werden in dem hier festgelegten Intervall auf neue Twitch-VODs geprueft. Neue VODs innerhalb des Alters-Fensters werden automatisch zur Download-Queue hinzugefuegt.</p>
+                        <div class="form-row" style="margin-bottom: 10px; align-items: center;">
+                            <span id="autoVodPollMinutesLabel" style="font-size:12px; color:var(--text-secondary);">Poll-Intervall (Minuten)</span>
+                            <input type="number" id="autoVodPollMinutes" min="5" max="360" value="15" style="width:90px;">
+                            <span id="autoVodMaxAgeHoursLabel" style="font-size:12px; color:var(--text-secondary); margin-left:12px;">Max. Alter (Stunden)</span>
+                            <input type="number" id="autoVodMaxAgeHours" min="1" max="720" value="24" style="width:90px;">
                         </div>
                     </div>