feat(epg): add global EPG display time offset (#1489)

Adds a global EPG display-time offset (Settings → EPG, whole minutes, ±720) for guides whose provider labels programme times with the wrong timezone. Display-only: parsed XMLTV values, SQLite rows, catch-up URLs and recording snapshots keep the provider's own times, so changing it needs no guide refresh. Closes the global part of #50.

The contract lives in `libs/shared/interfaces/src/lib/epg-display-offset.util.ts` with two equivalent forms: `epgDisplayTimeMs` shifts a programme for display, `epgProviderClockMs` shifts "now" into the provider's clock for every "currently airing" decision — the batched `GET_CURRENT_PROGRAMS_BATCH` lookup takes an explicit `nowMs`, and the channel lists, the Xtream/Stalker previews, the M3U player's current-programme mirror, the unified collection resolver, the dashboard live cards and the recording overlap all pick the same programme the guide renders as "now". Portal short-EPG windows start at the provider's own "now", so under a non-zero offset the Xtream preview surfaces cut their window from the full guide at the provider clock, Stalker short-EPG requests are widened for negative offsets, and every per-stream memory of the previous offset is retired together when the setting changes.

Co-authored-by: Mark Jardine <markjardine27@gmail.com>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

CLAUDE.md

@@ -1427,6 +1427,7 @@ stream_id`); it drops `series_id`/`movie_id`, so the builder pins the
 - XMLTV format support
 - Background parsing in worker thread
 - Stored in database for quick lookup
+- Global display-time offset (`Settings.epgOffsetMinutes`, Settings → EPG, ±720 min, Electron only): display-only, provider data is never rewritten. Two equivalent forms in `libs/shared/interfaces/src/lib/epg-display-offset.util.ts` — `epgDisplayTimeMs` (shift the programme; `ui/epg` rendering via the `offsetMinutes` input, channel rows, dashboard/recording labels; the programme dialog and multi-EPG overlay read the store themselves) and `epgProviderClockMs` (shift "now"; every "currently airing" decision: the `GET_CURRENT_PROGRAMS_BATCH` lookup takes an explicit `nowMs` and `EpgService` tags its cache with the offset, Xtream/Stalker/M3U current-programme selection and previews, the unified collection resolver, dashboard progress, recording overlap). A consumer applies exactly one form per comparison. Contract: `docs/architecture/m3u-playlist-module.md` ("EPG display offset")
 - Manual EPG mapping (Electron only): right-click a channel in any list (M3U views, Xtream portal list, Stalker ITV sidebar, global favorites) → "Map EPG channel" attaches it to an uploaded-XMLTV channel; stored in `epg_channel_mappings` keyed by the M3U lookup key or a playlist-scoped portal key (`xtream:{playlistId}:{id}` / `stalker:{playlistId}:{id}`, helpers in `libs/shared/interfaces/src/lib/epg-mapping-key.util.ts`); resolved on every EPG path (single + batch IPC lookups, portal detail views, preview queues); dialog: `libs/ui/components/src/lib/channel-list-container/epg-mapping-dialog/`
 
 **TMDB Metadata Enrichment** (opt-in):