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/lib/api.ts

@@ -0,0 +1,37 @@
+'use client';
+
+import useSWR from 'swr';
+import type { MeDTO } from '@musicshare/shared';
+
+export const API_URL = process.env.NEXT_PUBLIC_API_URL ?? 'http://localhost:4000';
+
+export class ApiError extends Error {
+  constructor(
+    public status: number,
+    message: string,
+  ) {
+    super(message);
+  }
+}
+
+export async function api<T = unknown>(path: string, init: { method?: string; body?: unknown } = {}): Promise<T> {
+  const res = await fetch(API_URL + path, {
+    method: init.method ?? (init.body ? 'POST' : 'GET'),
+    credentials: 'include',
+    headers: init.body !== undefined ? { 'content-type': 'application/json' } : undefined,
+    body: init.body !== undefined ? JSON.stringify(init.body) : undefined,
+  });
+  const data = await res.json().catch(() => ({}));
+  if (!res.ok) throw new ApiError(res.status, (data as { error?: string }).error ?? res.statusText);
+  return data as T;
+}
+
+export const fetcher = <T,>(path: string) => api<T>(path);
+
+export function useMe() {
+  const { data, error, isLoading, mutate } = useSWR<MeDTO, ApiError>('/me', fetcher, {
+    shouldRetryOnError: false,
+    revalidateOnFocus: false,
+  });
+  return { me: data, isLoading, loggedOut: error?.status === 401, mutate };
+}