fix(player): persist player prefs outside quota-bound queue blob (#958)

* fix(player): persist volume/repeat in dedicated localStorage key

Player prefs were bundled with the full queue blob in psysonic-player; after
thin-state #872 a large queue can exceed the quota and safeStorage silently
drops every write, so volume and repeat mode stopped surviving restarts.
Move them to psysonic_player_prefs, gate main-blob writes until rehydrate,
and sync volume to the Rust engine on startup.

* fix(player): split queue visibility and Last.fm cache from main persist blob

Move isQueueVisible and lastfmLovedCache to dedicated localStorage keys so
they keep saving when psysonic-player hits the quota on large queues. Include
the new keys in settings backup export.

* docs: note player prefs persist fix in CHANGELOG and credits (PR #958)

src/utils/export/backup.ts

@@ -17,6 +17,9 @@ const BACKUP_KEYS = [
   'psysonic-eq',
   'psysonic_global_shortcuts',
   'psysonic-player',
+  'psysonic_player_prefs',
+  'psysonic_queue_visible',
+  'psysonic_lastfm_loved_cache',
   'psysonic_home',
 ];