Absorbs VersionCheckController (/healthz poll + version parse) and
ServerHealthController (tri-state derive) into one signal-driven authority.
Adds the non-gating Unstable state across all ServerHealth branch sites
(OfflineGatedDataSource, SearchRepository, TrackRow, banner). Repoints
MinstrelApplication, MainActivity, PlayerFactory, VersionTooOldViewModel.
Drops the now-unused nowMs params the detekt UnusedParameter rule flagged.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
