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).

.github/copilot-instructions.md

@@ -6,6 +6,30 @@ Prefer explanations and refactors that align with these structures.
 
 Use this as your shared context when proposing changes. Keep edits minimal and match existing patterns referenced below.
 
+## TL;DR
+Small multi-service digital signage app (Flask API, React dashboard, MQTT scheduler). Edit `server/` for API logic, `scheduler/` for event publishing, and `dashboard/` for UI. If you're asking Copilot for changes, prefer focused prompts that include the target file(s) and the desired behavior.
+
+### How to ask Copilot
+- "Add a new route `GET /api/events/summary` that returns counts per event_type — implement in `server/routes/events.py`."
+- "Create an Alembic migration to add `duration` and `resolution` to `event_media` and update upload handler to populate them." 
+- "Refactor `scheduler/db_utils.py` to prefer precomputed EventMedia metadata and fall back to a HEAD probe." 
+- "Add an ffprobe-based worker that extracts duration/resolution/bitrate and stores them on `EventMedia`."
+
+### When not to change
+- Avoid editing generated assets under `dashboard/dist/` and compiled bundles. Don't modify files produced by CI or Docker builds (unless intentionally updating build outputs).
+
+### Contact / owner
+- Primary maintainer: RobbStarkAustria (owner). For architecture questions, ping the repo owner or open an issue and tag `@RobbStarkAustria`.
+
+### Important files (quick jump targets)
+- `scheduler/db_utils.py` — event formatting and scheduler-facing logic
+- `scheduler/scheduler.py` — scheduler main loop and MQTT publisher
+- `server/routes/eventmedia.py` — file uploads, streaming endpoint
+- `server/routes/events.py` — event CRUD and recurrence handling
+- `dashboard/src/components/CustomEventModal.tsx` — event creation UI
+- `dashboard/src/media.tsx` — FileManager / upload settings
+
+
 ## Big picture
 - Multi-service app orchestrated by Docker Compose.
   - API: Flask + SQLAlchemy (MariaDB), in `server/` exposed on :8000 (health: `/health`).
@@ -15,6 +39,16 @@ Use this as your shared context when proposing changes. Keep edits minimal and m
   - Scheduler: Publishes only currently active events (per group, at "now") to MQTT retained topics in `scheduler/scheduler.py`. It queries a future window (default: 7 days) to expand recurring events using RFC 5545 rules and applies event exceptions, but only publishes events that are active at the current time. When a group has no active events, the scheduler clears its retained topic by publishing an empty list. All time comparisons are UTC; any naive timestamps are normalized. Logging is concise; conversion lookups are cached and logged only once per media.
   - Nginx: Reverse proxy routes `/api/*` and `/screenshots/*` to API; everything else to dashboard (`nginx.conf`).
 
+  ## Recent changes since last commit
+
+  - Scheduler: when formatting video events the scheduler now performs a best-effort HEAD probe of the streaming URL and includes basic metadata in the emitted payload (mime_type, size, accept_ranges). Placeholders for richer metadata (duration, resolution, bitrate, qualities, thumbnails, checksum) are included for later population by a background worker.
+  - Streaming endpoint: a range-capable streaming endpoint was added at `/api/eventmedia/stream/<media_id>/<filename>` that supports byte-range requests (206 Partial Content) to enable seeking from clients.
+  - Event model & API: `Event` gained video-related fields (`event_media_id`, `autoplay`, `loop`, `volume`) and the API accepts and persists these when creating/updating video events.
+  - Dashboard: UI updated to allow selecting uploaded videos for events and to specify autoplay/loop/volume. File upload settings were increased (maxFileSize raised) and the client now validates video duration (max 10 minutes) before upload.
+  - FileManager: uploads compute basic metadata and enqueue conversions for office formats as before; video uploads now surface size and are streamable via the new endpoint.
+
+  Note: these edits are intentionally backwards-compatible — if the probe fails, the scheduler still emits the stream URL and the client should fallback to a direct play attempt or request richer metadata when available.
+
 ## Service boundaries & data flow
 - Database connection string is passed as `DB_CONN` (mysql+pymysql) to Python services.
   - API builds its engine in `server/database.py` (loads `.env` only in development).