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/m3uXtreamAdapter.js

@@ -58,6 +58,7 @@ class M3uXtreamAdapter {
                 name,
                 stream_icon,
                 stream_url,
+                program,
                 category_id,
                 added_at,
                 data
@@ -92,6 +93,7 @@ class M3uXtreamAdapter {
                 added: row.added_at,
                 // M3U-specific: direct stream URL (Xtream builds URLs from credentials)
                 stream_url: row.stream_url,
+                program: row.program || extra.program || null,
                 // Include extra fields from parser (tvgId, etc.)
                 epg_channel_id: extra.tvgId || null,
                 ...extra