Add Next.js frontend PWA

- Pages: login, register, tasks list, task detail
- Components: TaskCard, TaskForm, GroupSelector, StatusBadge, Header
- Tailwind CSS, dark/light mode, PWA manifest
- Running on :3001 via systemd

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/tasks/next.config.mjs

@@ -0,0 +1,15 @@
+/** @type {import("next").NextConfig} */
+const nextConfig = {
+  output: "standalone",
+  reactStrictMode: true,
+  async rewrites() {
+    return [
+      {
+        source: "/api/:path*",
+        destination: "http://localhost:3000/api/:path*",
+      },
+    ];
+  },
+};
+
+export default nextConfig;