fix(playback): pin queue playback to source server when browsing another library (#717)

* fix(playback): pin queue streams, cover art, and library links to queue server

When the active server changes while a queue from another server is playing,
keep streams and UI on queueServerId; switch back for artist/album links and
queue or player-bar context menus.

* fix(playback): switch to queue server when opening Now Playing

Ensure active server matches queueServerId before Subsonic fetches on the
Now Playing page, mobile player route, and queue info panel; scope caches
by server id.

* docs(credits): mention Now Playing in PR #717 contribution line

* fix(playback): route scrobble and queue sync to queue server

Address PR review: apiForServer for scrobble/now-playing/savePlayQueue,
clear queueServerId on server removal, mini-player queueServerId sync,
block cross-server enqueue with toast, and regression tests.

src/app/AppShell.tsx

@@ -1,5 +1,6 @@
 import React, { Suspense, useCallback, useEffect, useState } from 'react';
 import { useLocation, useNavigate } from 'react-router-dom';
+import { ensurePlaybackServerActive } from '../utils/playback/playbackServer';
 import { invoke } from '@tauri-apps/api/core';
 import { PanelRight } from 'lucide-react';
 import { useTranslation } from 'react-i18next';
@@ -97,7 +98,10 @@ export function AppShell() {
   useEffect(() => {
     const onPsyNavigate = (e: Event) => {
       const detail = (e as CustomEvent).detail;
-      if (detail?.to) navigate(detail.to);
+      if (!detail?.to) return;
+      void ensurePlaybackServerActive().then(ok => {
+        if (ok) navigate(detail.to);
+      });
     };
     window.addEventListener('psy:navigate', onPsyNavigate);
     return () => window.removeEventListener('psy:navigate', onPsyNavigate);