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/components/ChannelList.js

@@ -820,6 +820,8 @@ class ChannelList {
             this.groups = [];
         }
 
+        const source = await API.sources.getById(sourceId);
+
         // Use Xtream API endpoints - backend now supports M3U sources too
         const categories = await API.proxy.xtream.liveCategories(sourceId);
         const streams = await API.proxy.xtream.liveStreams(sourceId);
@@ -842,6 +844,9 @@ class ChannelList {
             tvgId: stream.epg_channel_id,
             tvgLogo: stream.stream_icon,
             url: stream.stream_url, // M3U has direct URLs
+            program: stream.program || null,
+            zapBeforeStreaming: source?.zapBeforeStreaming || false,
+            zapDelay: source?.zapDelay || 1500,
             groupId: `m3u_${sourceId}_${stream.category_id}`,
             groupTitle: categories.find(c => String(c.category_id) === String(stream.category_id))?.category_name || 'Uncategorized',
             sourceId,