v2.0.0: Multi-user authentication with JWT

Features:
- User registration and login with JWT tokens
- All data is now user-specific (multi-tenancy)
- Profile page with integrations and logout
- Automatic migration of existing data to first user

Backend changes:
- Added users and refresh_tokens tables
- Added user_id to all data tables (projects, entries, nodes, dictionaries, words, progress, configs, telegram_integrations, weekly_goals)
- JWT authentication middleware
- claimOrphanedData() for data migration

Frontend changes:
- AuthContext for state management
- Login/Register forms
- Profile page (replaced Integrations)
- All API calls use authFetch with Bearer token

Migration notes:
- On first deploy, backend automatically adds user_id columns
- First user to login claims all existing data

play-life-web/src/components/auth/AuthScreen.jsx

@@ -0,0 +1,16 @@
+import React, { useState } from 'react'
+import LoginForm from './LoginForm'
+import RegisterForm from './RegisterForm'
+
+function AuthScreen() {
+  const [mode, setMode] = useState('login') // 'login' or 'register'
+
+  if (mode === 'register') {
+    return <RegisterForm onSwitchToLogin={() => setMode('login')} />
+  }
+
+  return <LoginForm onSwitchToRegister={() => setMode('register')} />
+}
+
+export default AuthScreen
+