feat(slint): sidebar context menus, in-app toast, SearchView + Playlist Manager polish

Sidebar:
- Fix "Recursion detected" panic from focusing the playlist search input in init (defer via a single-shot Timer).
- Right-click context menus: playlist (Edit, Hide from sidebar, Move to folder with folder search + Move to root) and folder (Edit, Hide from sidebar), built on ContextMenu/ContextMenuItem; remove the unreachable hover "..." button.
- Filter hidden playlists/folders out of the list; add folders::set_folder_hidden.
- Folder list in the move-to-folder menu scrolls (cap 5 rows); close-on-click-outside so the folder-search input no longer dismisses the menu.
- Sort-menu Refresh now uses a dedicated refresh-cw icon.

Toast: in-app ToastKind/ToastState + Toast overlay mounted at the app root, crate::toast (show/hide, per-kind auto-hide via a reusable Timer, cross-thread *_weak helpers); surface play album/artist load failures.

SearchView: title inline with NavButtons + searchType filters floated right; tab strip on its own row; Most-popular hero for a track uses the new SearchTrackHero, sized to the artist card.

Playlist Manager: list view renders compact PmListRow rows instead of cards; grid/folder card fonts tightened to match Tauri; folder card centered with hover-reveal edit; search input narrowed to 70%.

cc

crates/qbz-slint/ui/app.slint

@@ -15,9 +15,10 @@ import { Theme } from "foundation/semantic-colors.slint";
 import { SplashScreen } from "splash/SplashScreen.slint";
 import { LoginScreen } from "login/LoginScreen.slint";
 import { AppShell } from "shell/AppShell.slint";
+import { Toast } from "primitives/Toast.slint";
 
 // Re-export the state globals so the Rust layer can populate them.
-export { HomeState, HomeActions, DiscoverBrowseState, DiscoverBrowseActions, ForYouState, MixState, GenreFilterState, GenreFilterActions, AlbumState, ArtistState, NavState, SessionState, SettingsState, AlbumActions, ArtistActions, ArtworkActions, NowPlayingState, QueueState, SearchState, SearchActions, NetworkSidebarState, NetworkSidebarActions, MusicianState, MusicianActions, LabelState, LabelActions, LocationViewState, LocationViewActions, FavoritesState, FavoritesActions, PlaylistPickerState, PlaylistPickerActions, PlaylistState, PlaylistActions, SidebarState, SidebarActions, CreatePlaylistState, CreatePlaylistActions, EditPlaylistState, EditPlaylistActions, CreateFolderState, CreateFolderActions, DragState, DragActions, PlaylistManagerState, PlaylistManagerActions, FolderEditState, FolderEditActions } from "state.slint";
+export { HomeState, HomeActions, DiscoverBrowseState, DiscoverBrowseActions, ForYouState, MixState, GenreFilterState, GenreFilterActions, AlbumState, ArtistState, NavState, SessionState, SettingsState, AlbumActions, ArtistActions, ArtworkActions, NowPlayingState, QueueState, SearchState, SearchActions, NetworkSidebarState, NetworkSidebarActions, MusicianState, MusicianActions, LabelState, LabelActions, LocationViewState, LocationViewActions, FavoritesState, FavoritesActions, PlaylistPickerState, PlaylistPickerActions, PlaylistState, PlaylistActions, SidebarState, SidebarActions, CreatePlaylistState, CreatePlaylistActions, EditPlaylistState, EditPlaylistActions, CreateFolderState, CreateFolderActions, DragState, DragActions, PlaylistManagerState, PlaylistManagerActions, FolderEditState, FolderEditActions, ToastState } from "state.slint";
 
 // Which top-level screen is shown. The app starts on `splash` while it
 // restores a saved session, then resolves to `shell` or `login`.
@@ -107,4 +108,12 @@ export component AppWindow inherits Window {
             root.close-app();
         }
     }
+
+    // App-global in-app toast overlay. Declared last so it floats over
+    // every screen (splash / login / shell). Driven by ToastState via
+    // crate::toast.
+    Toast {
+        width: 100%;
+        height: 100%;
+    }
 }