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/services/transcodeSession.js

@@ -230,8 +230,15 @@ class TranscodeSession extends EventEmitter {
         }
 
         // Map streams
-        args.push('-map', '0:v:0');
-        args.push('-map', '0:a:0?');
+        // Only map video/audio from the program: mapping the whole program pulls in
+        // DVB teletext/subtitle streams, which can't be encoded to HLS and kill FFmpeg
+        if (this.options.program) {
+            args.push('-map', `0:p:${this.options.program}:v:0`);
+            args.push('-map', `0:p:${this.options.program}:a:0?`);
+        } else {
+            args.push('-map', '0:v:0');
+            args.push('-map', '0:a:0?');
+        }
 
         // Add video encoder and filters based on selected encoder OR copy
         if (videoMode === 'copy') {