refactor(tray,config): own AppCaches from AppState, delete quarantine-era statics (#758, slice 2)

[Carme99]

Summary

Slice 2 of the behavioural-statics move: tray caches/mirrors + config quarantine/conflict flags now owned from AppState (SessionState carries AppCaches), QUARANTINE_TEST_LOCK deleted, MODE_ATOM_LOCK deleted. Isolation test proves two AppStates do not share caches. No behaviour change in the single-session path.

PARTIAL for #758 — do NOT close: LOCALE_TEST_LOCK survives (i18n::CURRENT stays process-wide per the issue step-3 keeps list); locale-table ownership is slice-3 scope.

What changed

• AppCaches threaded through tray (mod/cache/dedup/snooze/devices/actions), config (io/migrate/mod), updater_bg, cli, menu, polling/iteration, commands
• load_config/explain_rules take runtime-injected State/AppHandle (frontend invoke args unchanged)
• playback-state-changed listener consumes inline on the emitter thread (a spawn raced the rebuild and could paint a stale Play/Pause mark on same-track pause); guard pins the inline shape
• Process-wide keeps intact: TRAY handle, TRAY_WRITE_LOCK, i18n::CURRENT, macos CLAIMED, keychain/HTTP caches
• Stale LAST_*_STATE refs repointed to playing/shuffle/repeat_flag accessors

Tests

• cargo test --lib: 913/913 (new test_two_app_states_do_not_share_caches)
• cargo clippy --all-targets -D warnings: 0 errors
• cargo fmt --check: clean
• python3 docs/link-audit.py: clean

Review

Two independent critics scored the tree: 97/100 (2 comment-only gaps, both fixed) and 88/100 (P1 spawn-race, now inline with a guard; dead lock/static refs cleared). All gaps closed and re-verified (tray 36/36, lib 913/913).