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).
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