refactor(auth): E.44 — extract server-profile + lastfm + audio-settings factories (#609)

Three action-factories peel ~25 setters out of the authStore body,
following the playerStore action-factory pattern from Phase E:

- `createServerProfileActions` — `addServer`, `updateServer`,
  `removeServer` (the non-trivial one — drops every per-server map
  entry for the removed id), `setServers`, `setActiveServer`,
  `setLoggedIn`, `setConnecting`, `setConnectionError`, `logout`.
- `createAuthLastfmActions` — credentials + session connect/disconnect
  + error flag + master scrobbling toggle. Network calls (love /
  scrobble) stay in the playerStore-side `lastfmActions.ts`.
- `createAudioSettingsActions` — replay-gain / normalization /
  loudness mode toggles (each calls `usePlayerStore.getState()
  .updateReplayGainForCurrentTrack()` so a running track catches up),
  plus crossfade / gapless / hi-res / audio-output (no engine
  callback needed).

Pure code-move; no behaviour change. authStore.ts: 518 → 428 LOC (−90).

src/store/authLastfmActions.ts

@@ -0,0 +1,35 @@
+import type { AuthState } from './authStoreTypes';
+
+type SetState = (
+  partial: Partial<AuthState> | ((state: AuthState) => Partial<AuthState>),
+) => void;
+
+/**
+ * Last.fm account settings on the auth side: credentials, session
+ * connect/disconnect, error flag, and the master scrobbling toggle.
+ * The actual scrobble/love network calls live in `lastfmActions.ts`
+ * inside the playerStore — these here only manage the persisted
+ * account state.
+ */
+export function createAuthLastfmActions(set: SetState): Pick<
+  AuthState,
+  | 'setLastfm'
+  | 'connectLastfm'
+  | 'disconnectLastfm'
+  | 'setLastfmSessionError'
+  | 'setScrobblingEnabled'
+> {
+  return {
+    setLastfm: (apiKey, apiSecret, sessionKey, username) =>
+      set({ lastfmApiKey: apiKey, lastfmApiSecret: apiSecret, lastfmSessionKey: sessionKey, lastfmUsername: username }),
+
+    connectLastfm: (sessionKey, username) =>
+      set({ lastfmSessionKey: sessionKey, lastfmUsername: username }),
+
+    disconnectLastfm: () =>
+      set({ lastfmSessionKey: '', lastfmUsername: '', lastfmSessionError: false }),
+
+    setLastfmSessionError: (v) => set({ lastfmSessionError: v }),
+    setScrobblingEnabled: (v) => set({ scrobblingEnabled: v }),
+  };
+}