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/AddWords.jsx

@@ -1,9 +1,11 @@
 import React, { useState } from 'react'
+import { useAuth } from './auth/AuthContext'
 import './AddWords.css'
 
 const API_URL = '/api'
 
 function AddWords({ onNavigate, dictionaryId, dictionaryName }) {
+  const { authFetch } = useAuth()
   const [markdownText, setMarkdownText] = useState('')
   const [message, setMessage] = useState('')
   const [loading, setLoading] = useState(false)
@@ -81,7 +83,7 @@ function AddWords({ onNavigate, dictionaryId, dictionaryName }) {
         dictionary_id: dictionaryId !== undefined && dictionaryId !== null ? dictionaryId : undefined
       }))
 
-      const response = await fetch(`${API_URL}/words`, {
+      const response = await authFetch(`${API_URL}/words`, {
         method: 'POST',
         headers: {
           'Content-Type': 'application/json',