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>

public/js/pages/WatchPage.js

@@ -467,6 +467,7 @@ class WatchPage {
                     this.updateTranscodeStatus(statusMode, statusText);
                     if (this.playbackGeneration !== playbackGeneration) return;
                     const playlistUrl = await this.startTranscodeSession(url, {
+                        program: this.content?.program || this.content?.data?.program || null,
                         videoMode,
                         seekOffset: this.resumeTime, // Ensure seekOffset is passed
                         videoCodec: info.video,
@@ -508,6 +509,7 @@ class WatchPage {
             this.updateTranscodeStatus(statusMode, statusText);
             if (this.playbackGeneration !== playbackGeneration) return;
             const playlistUrl = await this.startTranscodeSession(url, {
+                program: this.content?.program || this.content?.data?.program || null,
                 videoMode: 'encode',
                 seekOffset: this.resumeTime
             });
@@ -533,6 +535,7 @@ class WatchPage {
 
             if (this.playbackGeneration !== playbackGeneration) return;
             const playlistUrl = await this.startTranscodeSession(url, {
+                program: this.currentChannel?.program || null,
                 videoMode: 'copy',
                 videoCodec,
                 seekOffset: this.resumeTime