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

README.md

@@ -63,7 +63,7 @@ Data flow summary:
 ### 🎯 **Event System**
 - **Presentations**: PowerPoint/LibreOffice → PDF conversion via Gotenberg
 - **Websites**: URL-based content display
-- **Videos**: Media file streaming
+ - **Videos**: Media file streaming with per-event playback settings (`autoplay`, `loop`, `volume`, `muted`); system-wide defaults configurable under Settings → Events → Videos
 - **Messages**: Text announcements
 - **WebUntis**: Educational schedule integration
    - Uses the system-wide Vertretungsplan/Supplement-Table URL (`supplement_table_url`) configured under Settings → Events. No separate per-event URL is required; WebUntis events display the same as Website events.
@@ -115,6 +115,17 @@ Data flow summary:
    # or: docker compose up -d --build
    ```
 
+Before running the dashboard dev server you may need to install Syncfusion packages used by the UI. Example (install only the packages you use):
+
+```bash
+# from the repository root
+cd dashboard
+npm install --save @syncfusion/ej2-react-splitbuttons @syncfusion/ej2-splitbuttons \
+   @syncfusion/ej2-react-grids @syncfusion/ej2-react-schedule @syncfusion/ej2-react-filemanager
+```
+
+License note: Syncfusion distributes components under a commercial license with a free community license for qualifying users. Verify licensing for your organization before using Syncfusion in production and document any license keys or compliance steps in this repository.
+
 4. **Initialize the database (first run only)**
    ```bash
    # One-shot: runs all Alembic migrations, creates default admin/group, and seeds academic periods
@@ -203,13 +214,18 @@ For detailed deployment instructions, see:
 - Website and WebUntis events share a unified payload:
    - `website`: `{ "type": "browser", "url": "https://..." }`
 - The `event_type` field remains specific (e.g., `presentation`, `website`, `webuntis`) so clients can dispatch appropriately; however, `website` and `webuntis` should be handled identically in clients.
+ - Videos include a `video` payload with a stream URL and playback flags:
+   - `video`: includes `url` (streaming endpoint) and `autoplay`, `loop`, `volume`, `muted`
+   - Streaming endpoint supports byte-range requests (206) to enable seeking: `/api/eventmedia/stream/<media_id>/<filename>`
   
 ## Recent changes since last commit
 
 - Video / Streaming support: Added end-to-end support for video events. The API and dashboard now allow creating `video` events referencing uploaded media. The server exposes a range-capable streaming endpoint at `/api/eventmedia/stream/<media_id>/<filename>` so clients can seek during playback.
 - Scheduler metadata: Scheduler now performs a best-effort HEAD probe for video stream URLs and includes basic metadata in the retained MQTT payload: `mime_type`, `size` (bytes) and `accept_ranges` (bool). Placeholders for richer metadata (`duration`, `resolution`, `bitrate`, `qualities`, `thumbnails`, `checksum`) are emitted as null/empty until a background worker fills them.
-- Dashboard & uploads: The dashboard's FileManager upload limits were increased (to support Full-HD uploads) and client-side validation enforces a maximum video length (10 minutes). The event modal exposes playback flags (`autoplay`, `loop`, `volume`).
-- DB model: `Event` includes new columns to store playback preferences (`autoplay`, `loop`, `volume`) and reference uploaded media via `event_media_id`.
+- Dashboard & uploads: The dashboard's FileManager upload limits were increased (to support Full-HD uploads) and client-side validation enforces a maximum video length (10 minutes). The event modal exposes playback flags (`autoplay`, `loop`, `volume`, `muted`) and initializes them from system defaults for new events.
+- DB model & API: `Event` includes `muted` in addition to `autoplay`, `loop`, and `volume`; endpoints accept, persist, and return these fields for video events. Events reference uploaded media via `event_media_id`.
+- Settings UI: Settings page refactored to nested tabs; added Events → Videos defaults (autoplay, loop, volume, mute) backed by system settings keys (`video_autoplay`, `video_loop`, `video_volume`, `video_muted`).
+- Academic Calendar UI: Merged “School Holidays Import” and “List” into a single “📥 Import & Liste” tab; nested tab selection is persisted with controlled `selectedItem` state to avoid jumps.
 
 These changes are designed to be safe if metadata extraction or probes fail — clients should still attempt playback using the provided `url` and fall back to requesting/resolving richer metadata when available.
 
@@ -309,6 +325,7 @@ mosquitto_sub -h localhost -t "infoscreen/+/heartbeat" -v
 - `GET /api/files/converted/{path}` - Download converted PDFs
 - `POST /api/conversions/{media_id}/pdf` - Request conversion
 - `GET /api/conversions/{media_id}/status` - Check conversion status
+ - `GET /api/eventmedia/stream/<media_id>/<filename>` - Stream media with byte-range support (206) for seeking
 
 ### System Settings
 - `GET /api/system-settings` - List all system settings (admin+)
@@ -321,6 +338,11 @@ mosquitto_sub -h localhost -t "infoscreen/+/heartbeat" -v
       - `presentation_interval` (seconds, default "10")
       - `presentation_page_progress` ("true"/"false", default "true")
       - `presentation_auto_progress` ("true"/"false", default "true")
+   - Video defaults stored as keys:
+      - `video_autoplay` ("true"/"false", default "true")
+      - `video_loop` ("true"/"false", default "true")
+      - `video_volume` (0.0–1.0, default "0.8")
+      - `video_muted` ("true"/"false", default "false")
 
 ### Health & Monitoring
 - `GET /health` - Service health check
@@ -353,10 +375,12 @@ mosquitto_sub -h localhost -t "infoscreen/+/heartbeat" -v
 - **Events**: Schedule management
 - **Media**: File upload and conversion
 - **Settings**: Central configuration (tabbed)
-   - 📅 Academic Calendar (all users): School Holidays import/list and Academic Periods (set active period)
+   - 📅 Academic Calendar (all users):
+      - 📥 Import & Liste: CSV/TXT import combined with holidays list
+      - 🗂️ Perioden: Academic Periods (set active period)
    - 🖥️ Display & Clients (admin+): Defaults placeholders and quick links to Clients/Groups
    - 🎬 Media & Files (admin+): Upload settings placeholders and Conversion status overview
-   - 🗓️ Events (admin+): WebUntis/Vertretungsplan URL enable/disable, save, preview. Presentations: general defaults for slideshow interval, page-progress, and auto-progress; persisted via `/api/system-settings` keys and applied on create in the event modal.
+   - 🗓️ Events (admin+): WebUntis/Vertretungsplan URL enable/disable, save, preview. Presentations: general defaults for slideshow interval, page-progress, and auto-progress; persisted via `/api/system-settings` keys and applied on create in the event modal. Videos: system-wide defaults for `autoplay`, `loop`, `volume`, and `muted`; persisted via `/api/system-settings` keys and applied on create in the event modal.
    - ⚙️ System (superadmin): Organization info and Advanced configuration placeholders
 - **Holidays**: Academic calendar management
  - **Program info**: Version, build info, tech stack and paginated changelog (reads `dashboard/public/program-info.json`)