Add end-to-end catch-up support for XC clients and native apps: provider
proxy with failover and per-viewer session pooling, REST session minting
for tokenless playback URLs, catch-up admin stats, combined connection
stats, and Stats UI with dedicated cards plus websocket updates.
Includes Redis namespace consolidation under timeshift:* (dropping legacy
timeshift_ id prefixes), dedicated catch-up stop by session_id, and
cleaner channel/client metadata split for stats keys.
Closes#133
- Removed dead VOD URL routes: `VODPlaylistView` (playlist generation), `VODPositionView` (position tracking), and the class-based `VODStatsView` (replaced by the existing function-based `vod_stats` view).
- Removed dead `updateVODPosition()` API method from `frontend/src/api.js`, which called the now-removed position tracking endpoint.
