feat: precompute stream grouping during source sync (#13)

Move variant grouping work out of Live TV rendering into the
catalog pipeline: a liveProjectionService builds the logical channel
projection (schema in liveProjectionSchema) whenever a source is
added, synced or modified (name change, new address), and the
projection is served through a /live route. ChannelList now consumes
the precomputed projection via a liveChannelProjection client
service, recalculating only when the catalog changes. Cover
projection building, incremental recompute and client consumption
with tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/css/main.css

@@ -863,7 +863,8 @@ h4 {
   margin: var(--space-md) 0;
 }
 
-.laya-language-notice {
+.laya-language-notice,
+.live-projection-notice {
   margin: var(--space-sm) var(--space-md);
   padding: var(--space-sm);
   border-radius: var(--radius-sm);