Three file-private helpers + their shared module-scoped track id move
into src/store/playbackUrlRouting.ts: recordEnginePlayUrl,
playbackSourceHintForResolvedUrl, shouldRebindPlaybackToHotCache. The
`lastOpenedWithHttpTrackId` mutable goes with them — only those three
read it. No external callers, no re-exports needed.
Adds 12 focused tests covering the source-kind classifier
(stream / hot / offline), the rebind decision across stream:-prefix
forms, the empty-serverId / un-recorded edge cases, and the
test-only reset helper.
playerStore 3490 → 3470 LOC.
Frank Stellmacher