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).

server/wsgi.py

@@ -19,6 +19,10 @@ sys.path.append('/workspace')
 
 app = Flask(__name__)
 
+# Allow uploads up to 1 GiB at the Flask level (application hard limit)
+# See nginx.conf for proxy limit; keep both in sync.
+app.config['MAX_CONTENT_LENGTH'] = 1 * 1024 * 1024 * 1024  # 1 GiB
+
 # Configure Flask session
 # In production, use a secure random key from environment variable
 app.config['SECRET_KEY'] = os.environ.get('FLASK_SECRET_KEY', 'dev-secret-key-change-in-production')