feat(cli): completions, library/audio commands, server switcher

Embed bash and zsh completion scripts and add a `completions` subcommand.
Extend the player CLI (library, audio device, instant mix) and surface
`music_library` in snapshots. Add a shared active-server switcher in the
header and locales; instant mix can reseed the queue from CLI and UI.

src/utils/switchActiveServer.ts

@@ -0,0 +1,30 @@
+import { pingWithCredentials, scheduleInstantMixProbeForServer } from '../api/subsonic';
+import type { ServerProfile } from '../store/authStore';
+import { useAuthStore } from '../store/authStore';
+import { usePlayerStore } from '../store/playerStore';
+
+/**
+ * Ping, update server identity / Instant Mix probe, set active server, clear local playback
+ * and pull the new server's saved play queue.
+ */
+export async function switchActiveServer(server: ServerProfile): Promise<boolean> {
+  try {
+    const ping = await pingWithCredentials(server.url, server.username, server.password);
+    if (!ping.ok) return false;
+    const identity = {
+      type: ping.type,
+      serverVersion: ping.serverVersion,
+      openSubsonic: ping.openSubsonic,
+    };
+    const auth = useAuthStore.getState();
+    auth.setSubsonicServerIdentity(server.id, identity);
+    scheduleInstantMixProbeForServer(server.id, server.url, server.username, server.password, identity);
+    auth.setActiveServer(server.id);
+    auth.setLoggedIn(true);
+    usePlayerStore.getState().clearQueue();
+    await usePlayerStore.getState().initializeFromServerQueue();
+    return true;
+  } catch {
+    return false;
+  }
+}