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
