Adds the hide-track capability. Repository wraps QuarantineApi.flag
with the QUARANTINE_FLAG mutation-queue fallback mirroring the
existing unflag pattern. Sheet collects reason (FilterChip row) +
optional notes (OutlinedTextField); reason vocabulary matches the
server wire values (bad_rip / wrong_file / wrong_tags / duplicate /
other) exactly.
Not yet reachable from a user surface — TrackActionsSheet wires it
in the next commit.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>