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).

nginx.conf

@@ -9,6 +9,11 @@ http {
     server {
         listen 80;
         server_name _;
+        # Allow larger uploads (match Flask MAX_CONTENT_LENGTH); adjust as needed
+        client_max_body_size 1G;
+        # Increase proxy timeouts for long uploads on slow connections
+        proxy_read_timeout 3600s;
+        proxy_send_timeout 3600s;
 
         # Leitet /api/ und /screenshots/ an den API-Server weiter
         location /api/ {
@@ -17,6 +22,29 @@ http {
         location /screenshots/ {
             proxy_pass http://infoscreen_api/screenshots/;
         }
+        # Public direct serving (optional)
+        location /files/ {
+            alias /opt/infoscreen/server/media/;
+            sendfile on;
+            tcp_nopush on;
+            types {
+                video/mp4 mp4;
+                video/webm webm;
+                video/ogg ogg;
+            }
+            add_header Accept-Ranges bytes;
+            add_header Cache-Control "public, max-age=3600";
+        }
+
+        # Internal location for X-Accel-Redirect (protected)
+        location /internal_media/ {
+            internal;
+            alias /opt/infoscreen/server/media/;
+            sendfile on;
+            tcp_nopush on;
+            add_header Accept-Ranges bytes;
+            add_header Cache-Control "private, max-age=0, s-maxage=3600";
+        }
         # Alles andere geht ans Frontend
         location / {
             proxy_pass http://dashboard;