Add Flask/Python backend server

- Create app.py with Flask server on port 5002
- Add requirements.txt with Python dependencies
- Add run_flask.bat for Windows users
- Add run_flask.sh for Linux/Mac users
- Complete Flask setup documentation
- Database integration with PyMySQL
- Full LLM API support (Gemini, DeepSeek, OpenAI, Claude)
- CORS configuration
- Error handling middleware

Features:
✅ Runs on http://127.0.0.1:5002
✅ All LLM APIs supported
✅ Database connection
✅ API proxy for CORS fix
✅ Auto setup scripts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

requirements.txt

@@ -0,0 +1,27 @@
+# Flask 核心
+Flask==3.0.0
+Werkzeug==3.0.1
+
+# CORS 支援
+Flask-Cors==4.0.0
+
+# 資料庫
+PyMySQL==1.1.0
+cryptography==41.0.7
+
+# HTTP 請求
+requests==2.31.0
+
+# 環境變數
+python-dotenv==1.0.0
+
+# JSON 處理
+jsonschema==4.20.0
+
+# 日期時間
+python-dateutil==2.8.2
+
+# 開發工具（可選）
+# pytest==7.4.3
+# black==23.12.1
+# flake8==6.1.0