Add Next.js web app

Feed with live updates and pinning, profiles with follow/pin, featured song
picker, settings for all music services, and account deletion.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8

apps/web/src/components/Nav.tsx

@@ -0,0 +1,41 @@
+'use client';
+
+import Link from 'next/link';
+import { useRouter } from 'next/navigation';
+import { api, useMe } from '@/lib/api';
+
+export function Nav() {
+  const { me, mutate } = useMe();
+  const router = useRouter();
+  const logout = async () => {
+    await api('/auth/logout', { method: 'POST', body: {} });
+    await mutate(undefined, { revalidate: true });
+    router.push('/');
+  };
+  return (
+    <nav className="nav">
+      <Link href="/" className="brand">
+        musicshare
+      </Link>
+      <div className="nav-links">
+        {me ? (
+          <>
+            <Link href="/">Feed</Link>
+            <Link href={`/u/${me.username}`}>Profile</Link>
+            <Link href="/settings">Settings</Link>
+            <button className="link-button" onClick={logout}>
+              Log out
+            </button>
+          </>
+        ) : (
+          <>
+            <Link href="/login">Log in</Link>
+            <Link href="/register" className="btn btn-primary">
+              Sign up
+            </Link>
+          </>
+        )}
+      </div>
+    </nav>
+  );
+}