feat(library): exclude chosen folders from music browsing

Replaces `src/lib/utils/podcastFilter.ts` — a shipped personal workaround
that dropped any item whose name, album, album artist or artist was
literally "Podcasts" — with a real user setting applied in Rust.

The old filter was wrong twice over: it hardcoded one user's folder
layout keyed on an English literal, and it put a domain rule (what a
query should return) in the presentation layer. It slipped past
`check:boundary` only because it matched on names rather than on an
item-type array.

- `repository::exclusions` owns the rule and the process-wide id set,
  the same shape as `online::STREAMING_QUALITY` so it survives a
  repository being rebuilt on re-login.
- `HybridRepository` applies it where the cache and server legs of every
  cache-first query converge (`parallel_race` / `race_with_refresh`),
  plus the bespoke `get_items` path and the server-only reads. Filtering
  before the "has content" check is what makes a cache page of nothing
  but hidden items fall through to the server.
- Exclusion is by stable item id, never by name, and matches an item's
  own id or any container link it carries (parent, album, library,
  series, season, artist).
- A direct `get_item` lookup and the Downloads surface are deliberately
  unfiltered: hiding those would break playback and file management of
  anything inside a hidden folder.
- `LibrarySettings` persists to `app_settings` and is restored in the
  setup hook, alongside the streaming-quality cap. Default is an empty
  list — nobody inherits the old "Podcasts" behaviour.
- New commands `library_get_settings`, `library_set_settings` and
  `library_get_exclusion_candidates`; the candidates read goes through
  `get_items_unfiltered` so an already-hidden folder still appears in the
  picker and the setting can be undone.
- Settings page gains a "Hidden Folders" section that renders the
  backend's candidate list and sends back ticked ids; it decides nothing.

TRACES: UR-076 | DR-209 | UT-203

src-tauri/src/lib.rs

@@ -79,6 +79,10 @@ use commands::{
     get_smart_cache_stats,
     image_get_url,
     is_item_pinned,
+    // Library browsing preferences (hidden folders)
+    library_get_exclusion_candidates,
+    library_get_settings,
+    library_set_settings,
     lms_create_sync_group,
     lms_dissolve_sync_group,
     // LMS multi-room sync group commands
@@ -884,6 +888,10 @@ fn specta_builder() -> Builder<tauri::Wry> {
             sync_full_catalog,
             catalog_sync_status,
             set_show_server_catalog,
+            // Library browsing preferences (UR-076 / DR-209)
+            library_get_settings,
+            library_set_settings,
+            library_get_exclusion_candidates,
             resume_queued_downloads,
             get_download_manager_stats,
             set_max_concurrent_downloads,
@@ -1312,6 +1320,18 @@ pub fn run() {
                 });
             }
 
+            // Restore the folders the user hid from browsing, for the same
+            // reason and in the same way. Until it lands nothing is hidden —
+            // the pre-existing behaviour — and no query can have run this early.
+            //
+            // TRACES: UR-076 | DR-209
+            {
+                let handle = app.handle().clone();
+                tauri::async_runtime::spawn(async move {
+                    crate::commands::restore_library_settings(&handle).await;
+                });
+            }
+
             // Initialize thumbnail cache
             info!("[INIT] Initializing thumbnail cache...");
             let app_data_dir = if let Ok(test_data_dir) = std::env::var("JELLYTAU_DATA_DIR") {