feat(video): add streamable video events & dashboard controls

Add end-to-end support for video events: server streaming, scheduler
metadata, API fields, and dashboard UI.

- Server: range-capable streaming endpoint with byte-range support.
- Scheduler: emits `video` object; best-effort HEAD probe adds
  `mime_type`, `size`, `accept_ranges`; placeholders for richer
  metadata (duration/resolution/bitrate/qualities/thumbnails).
- API/DB: accept and persist `event_media_id`, `autoplay`, `loop`,
  `volume` for video events.
- Frontend: Event modal supports video selection + playback options;
  FileManager increased upload size and client-side duration check
  (max 10 minutes).
- Docs/UX: bumped program-info, added UX-only changelog and updated
  Copilot instructions for contributors.
- Notes: metadata extraction (ffprobe), checksum persistence, and
  HLS/DASH transcoding are recommended follow-ups (separate changes).

README.md

@@ -203,6 +203,15 @@ 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.
+  
+## 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`.
+
+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.
 
 See `MQTT_EVENT_PAYLOAD_GUIDE.md` for details.
   - `infoscreen/{uuid}/group_id` - Client group assignment