feat(settings): wire Playback + Scrobbling panels to the backend

Adds src/api/endpoints/settings.ts (getSettings/updateSettings,
getScrobbling/updateScrobbling) plus AppSettings/ScrobblingConfig types
and a Settings cache tag. Replaces the "coming soon" scaffolds:

- Playback: stream-quality preference (SegmentedControl), server-synced.
- Scrobbling: enable + provider (Last.fm/ListenBrainz) + username +
  write-only session key, with a linked/not-linked badge and save states.

Built with modern-sk (Window/SegmentedControl/TextField/Button/Callout/
Badge) + the shared Loading/Error states; en + ru strings added. Server
state flows through RTK Query hooks only (no fetch in components).

Also drops a pre-existing unused TextField import in LibraryPage that was
failing `tsc --noEmit`.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/api/endpoints/settings.ts

@@ -0,0 +1,90 @@
+import { api } from '../index';
+import type {
+  AppSettings,
+  ScrobbleProvider,
+  ScrobblingConfig,
+  StreamQuality,
+  ThemePref,
+} from '../types';
+
+// Wire shapes (snake_case) from the backend, mapped to the app's camelCase types.
+interface RawSettings {
+  theme: ThemePref;
+  stream_quality: StreamQuality;
+}
+interface RawScrobbling {
+  enabled: boolean;
+  provider: ScrobbleProvider | null;
+  username: string | null;
+  configured: boolean;
+}
+
+const toSettings = (r: RawSettings): AppSettings => ({
+  theme: r.theme,
+  streamQuality: r.stream_quality,
+});
+const toScrobbling = (r: RawScrobbling): ScrobblingConfig => ({
+  enabled: r.enabled,
+  provider: r.provider,
+  username: r.username,
+  configured: r.configured,
+});
+
+export const settingsApi = api.injectEndpoints({
+  endpoints: (build) => ({
+    getSettings: build.query<AppSettings, void>({
+      query: () => '/settings',
+      transformResponse: (raw: RawSettings) => toSettings(raw),
+      providesTags: ['Settings'],
+    }),
+    updateSettings: build.mutation<
+      AppSettings,
+      { theme?: ThemePref; streamQuality?: StreamQuality }
+    >({
+      query: ({ theme, streamQuality }) => ({
+        url: '/settings',
+        method: 'PATCH',
+        body: { theme, stream_quality: streamQuality },
+      }),
+      transformResponse: (raw: RawSettings) => toSettings(raw),
+      invalidatesTags: ['Settings'],
+    }),
+    getScrobbling: build.query<ScrobblingConfig, void>({
+      query: () => '/settings/scrobbling',
+      transformResponse: (raw: RawScrobbling) => toScrobbling(raw),
+      providesTags: ['Settings'],
+    }),
+    updateScrobbling: build.mutation<
+      ScrobblingConfig,
+      {
+        enabled: boolean;
+        provider: ScrobbleProvider | null;
+        username: string | null;
+        // Write-only: send only when the user typed a new key; omit to keep the
+        // stored one (the server never returns it).
+        sessionKey?: string;
+      }
+    >({
+      query: ({ enabled, provider, username, sessionKey }) => ({
+        url: '/settings/scrobbling',
+        method: 'PUT',
+        body: {
+          enabled,
+          provider,
+          username,
+          session_key: sessionKey,
+        },
+      }),
+      transformResponse: (raw: RawScrobbling) => toScrobbling(raw),
+      invalidatesTags: ['Settings'],
+    }),
+  }),
+  overrideExisting: false,
+});
+
+export const {
+  useGetSettingsQuery,
+  useUpdateSettingsMutation,
+  useGetScrobblingQuery,
+  useUpdateScrobblingMutation,
+} = settingsApi;

src/api/index.ts

@@ -23,6 +23,7 @@ export const api = createApi({
     'Like',
     'User',
     'Storage',
+    'Settings',
   ],
   // Tier 2 offline: seed the cache from the persisted snapshot dispatched at
   // startup (see `store/rtkqPersist.ts`). Returning the saved queries/mutations

src/api/types.ts

@@ -258,3 +258,24 @@ export interface MetadataEdit {
   genre?: string;
   trackNumber?: number;
 }
+
+// -- user settings (`/settings`) ---------------------------------------------
+export type ThemePref = 'system' | 'light' | 'dark';
+export type StreamQuality = 'original' | 'high' | 'medium' | 'low';
+
+/** General per-user preferences from `GET /settings`. */
+export interface AppSettings {
+  theme: ThemePref;
+  streamQuality: StreamQuality;
+}
+
+export type ScrobbleProvider = 'lastfm' | 'listenbrainz';
+
+/** Scrobbling config from `GET /settings/scrobbling`. The session key is
+ * write-only server-side, so it never appears here — only `configured`. */
+export interface ScrobblingConfig {
+  enabled: boolean;
+  provider: ScrobbleProvider | null;
+  username: string | null;
+  configured: boolean;
+}