Add Enigma2/OpenWebif M3U support: program mapping and zap-before-streaming

- Parse #EXTVLCOPT:program=N from M3U playlists (both full and streaming
  parsers, per channel, strict mode) and store it on playlist items
- Transcode multi-program MPEG-TS streams by mapping only the selected
  program's first video and audio stream (DVB teletext/subtitles in the
  program otherwise make FFmpeg fail to produce HLS)
- Optional per-source "zap before streaming" with configurable delay:
  POST /api/openwebif/zap takes sourceId + streamId, requires an enabled,
  zap-enabled M3U source containing that channel, derives the receiver
  from the configured source URL (never from the client), validates the
  Enigma2 service reference, uses a timeout without redirects and does
  not echo the receiver response
- Live TV: Stop button, and stop playback when leaving the page
- Tests for ordinary and program-tagged playlists and the zap endpoint

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/db/sqlite.js

@@ -145,6 +145,13 @@ function initSchema() {
         // Column already exists, ignore
     }
 
+    try {
+        db.exec(`ALTER TABLE playlist_items ADD COLUMN program TEXT`);
+        console.log('[SQLite] Added program column to playlist_items');
+    } catch (e) {
+        // Column already exists, ignore
+    }
+    
     console.log('[SQLite] Schema initialized');
 }