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/lib/auth.ts

@@ -0,0 +1,56 @@
+"use client";
+
+import { createContext, useContext } from "react";
+import { User } from "./api";
+
+export interface AuthState {
+  token: string | null;
+  user: User | null;
+  setAuth: (token: string | null, user: User | null) => void;
+  logout: () => void;
+}
+
+export const AuthContext = createContext<AuthState>({
+  token: null,
+  user: null,
+  setAuth: () => {},
+  logout: () => {},
+});
+
+export function useAuth() {
+  return useContext(AuthContext);
+}
+
+export function getStoredToken(): string | null {
+  if (typeof window === "undefined") return null;
+  return localStorage.getItem("taskteam_token");
+}
+
+export function setStoredToken(token: string | null) {
+  if (typeof window === "undefined") return;
+  if (token) {
+    localStorage.setItem("taskteam_token", token);
+  } else {
+    localStorage.removeItem("taskteam_token");
+  }
+}
+
+export function getStoredUser(): User | null {
+  if (typeof window === "undefined") return null;
+  const raw = localStorage.getItem("taskteam_user");
+  if (!raw) return null;
+  try {
+    return JSON.parse(raw);
+  } catch {
+    return null;
+  }
+}
+
+export function setStoredUser(user: User | null) {
+  if (typeof window === "undefined") return;
+  if (user) {
+    localStorage.setItem("taskteam_user", JSON.stringify(user));
+  } else {
+    localStorage.removeItem("taskteam_user");
+  }
+}