feat(video, settings, docs): add muted playback, nested Settings tabs, merge holidays tab; bump 2025.1.0-alpha.11

API/DB: add Event.muted with full CRUD wiring (Alembic migration), persist/return with autoplay/loop/volume
Dashboard: per‑event video options (autoplay/loop/volume/muted) with system defaults; Settings → Events → Videos defaults
Settings UX: nested tabs with controlled selection; Academic Calendar: merge “Schulferien Import”+“Liste” into “📥 Import & Liste”
Docs: update README and copilot-instructions (video payload, streaming 206, defaults keys); update program-info.json changelog; bump version to 2025.1.0‑alpha.11

server/init_defaults.py

@@ -50,6 +50,9 @@ with engine.connect() as conn:
             ('presentation_interval', '10', 'Standard Intervall für Präsentationen (Sekunden)'),
             ('presentation_page_progress', 'true', 'Seitenfortschrift anzeigen (Page-Progress) für Präsentationen'),
             ('presentation_auto_progress', 'true', 'Automatischer Fortschritt (Auto-Progress) für Präsentationen'),
+            ('video_autoplay', 'true', 'Autoplay (automatisches Abspielen) für Videos'),
+            ('video_loop', 'true', 'Loop (Wiederholung) für Videos'),
+            ('video_volume', '0.8', 'Standard Lautstärke für Videos (0.0 - 1.0)'),
         ]
     
         for key, value, description in default_settings: