Phase 1: auth, room CRUD, WebSocket chat, PWA frontend

Invite-only FastAPI + SQLAlchemy(async) + Postgres backend (session-cookie
auth via CLI-provisioned accounts, open-room CRUD, single-instance /ws/chat)
and a React + Vite PWA frontend (login, room list, chat view). Backend tests
pass against a local Postgres DB. See README.md and backend/README.md for
setup, and ARCHITECTURE.md for the full phased design.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/context/AuthContext.tsx

@@ -0,0 +1,51 @@
+import { createContext, useContext, useEffect, useState, type ReactNode } from 'react'
+import * as authApi from '../api/auth'
+import { ApiError } from '../api/client'
+import type { User } from '../types'
+
+interface AuthContextValue {
+  user: User | null
+  loading: boolean
+  login: (usernameOrEmail: string, password: string) => Promise<void>
+  logout: () => Promise<void>
+}
+
+const AuthContext = createContext<AuthContextValue | undefined>(undefined)
+
+export function AuthProvider({ children }: { children: ReactNode }) {
+  const [user, setUser] = useState<User | null>(null)
+  const [loading, setLoading] = useState(true)
+
+  useEffect(() => {
+    authApi
+      .me()
+      .then(setUser)
+      .catch((err) => {
+        if (!(err instanceof ApiError && err.status === 401)) {
+          console.error('Failed to load current user', err)
+        }
+      })
+      .finally(() => setLoading(false))
+  }, [])
+
+  async function login(usernameOrEmail: string, password: string) {
+    setUser(await authApi.login(usernameOrEmail, password))
+  }
+
+  async function logout() {
+    await authApi.logout()
+    setUser(null)
+  }
+
+  return (
+    <AuthContext.Provider value={{ user, loading, login, logout }}>
+      {children}
+    </AuthContext.Provider>
+  )
+}
+
+export function useAuth(): AuthContextValue {
+  const ctx = useContext(AuthContext)
+  if (!ctx) throw new Error('useAuth must be used within an AuthProvider')
+  return ctx
+}