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>

run_flask.bat

@@ -0,0 +1,59 @@
+@echo off
+REM Flask 伺服器啟動腳本
+
+echo ========================================
+echo HR Performance System - Flask Server
+echo ========================================
+echo.
+
+REM 檢查 Python 是否安裝
+python --version >nul 2>&1
+if errorlevel 1 (
+    echo [ERROR] Python is not installed or not in PATH
+    echo Please install Python 3.8 or higher
+    pause
+    exit /b 1
+)
+
+REM 檢查虛擬環境
+if not exist "venv\" (
+    echo [INFO] Creating virtual environment...
+    python -m venv venv
+    if errorlevel 1 (
+        echo [ERROR] Failed to create virtual environment
+        pause
+        exit /b 1
+    )
+    echo [SUCCESS] Virtual environment created
+    echo.
+)
+
+REM 啟動虛擬環境
+echo [INFO] Activating virtual environment...
+call venv\Scripts\activate.bat
+
+REM 安裝依賴
+echo [INFO] Installing dependencies...
+pip install -r requirements.txt
+if errorlevel 1 (
+    echo [ERROR] Failed to install dependencies
+    pause
+    exit /b 1
+)
+echo.
+
+REM 檢查 .env 檔案
+if not exist ".env" (
+    echo [WARNING] .env file not found
+    echo Please create .env file with required configuration
+    echo.
+)
+
+REM 啟動 Flask 伺服器
+echo [INFO] Starting Flask server...
+echo Server will run on http://127.0.0.1:5002
+echo Press Ctrl+C to stop the server
+echo.
+python app.py
+
+pause