feat: per-streamer storage stats panel — see what eats the disk

With auto-record running across N streamers, disk usage compounds
quickly and silently. New Settings -> Storage card walks the
download folder once per Refresh click and shows per-streamer
totals so the user can decide which folders to thin out.

Server:
- new computeStorageStats() — readdirSync the download_path top
  level, classify each subfolder as a known streamer (matches
  config.streamers case-insensitive), the special "Clips" bucket,
  or extra (unknown user-created folder, surfaced separately so
  it does not get conflated with archive bytes). Recursive
  walkFolderForStats counts files + total bytes + live-only bytes
  (subfolder named "live" — populated by the live-recording
  feature) + chat bytes (anything matching .chat.json or
  .chat.jsonl). Skips per-entry on permission errors so a single
  blocked folder can not abort the whole scan.
- Sort order: largest first, both for streamers and extras.
- IPC get-storage-stats returns the structured result.

Renderer:
- Settings card with a Refresh button + summary line ("X files,
  Y bytes, free disk Z") + two tables (known-streamers, then
  extras) with columns for file count, total bytes, live bytes,
  chat bytes, and a per-row Open button that drops the user
  straight into Explorer at that folder.
- Tables built via createElement (no innerHTML) so a streamer
  named with HTML special chars cannot escape the cell.
- DE + EN labels for everything; column headers and the Open
  button locale-switch on the fly.

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

src/index.html

@@ -596,6 +596,16 @@
                         <pre id="debugLogOutput" class="log-panel">Lade...</pre>
                     </div>
 
+                    <div class="settings-card">
+                        <div class="form-row" style="align-items:center; justify-content:space-between; margin-bottom: 10px;">
+                            <h3 id="storageCardTitle" style="margin:0;">Storage</h3>
+                            <button class="btn-secondary" id="btnRefreshStorage" onclick="refreshStorageStats()">Aktualisieren</button>
+                        </div>
+                        <p id="storageCardIntro" style="color: var(--text-secondary); font-size:13px; margin-bottom:12px; line-height:1.5;">Disk-Verbrauch pro Streamer im aktuellen Download-Ordner. Live-Aufnahmen werden separat ausgewiesen.</p>
+                        <div id="storageSummary" style="color: var(--text-secondary); font-size:12px; margin-bottom:8px;"></div>
+                        <div id="storageList"></div>
+                    </div>
+
                     <div class="settings-card">
                         <h3 id="discordCardTitle">Discord-Webhook</h3>
                         <p id="discordCardIntro" style="color: var(--text-secondary); font-size:13px; margin-bottom:12px; line-height:1.5;">Sende Benachrichtigungen an einen Discord-Channel via Webhook — nuetzlich fuer Multi-Device-Setups oder eine dedizierte Archiv-Maschine.</p>