feat: HR Portal - Complete Multi-Tenant System with Redis Session Storage

Major Features:
- ✅ Multi-tenant architecture (tenant isolation)
- ✅ Employee CRUD with lifecycle management (onboarding/offboarding)
- ✅ Department tree structure with email domain management
- ✅ Company info management (single-record editing)
- ✅ System functions CRUD (permission management)
- ✅ Email account management (multi-account per employee)
- ✅ Keycloak SSO integration (auth.lab.taipei)
- ✅ Redis session storage (10.1.0.254:6379)
  - Solves Cookie 4KB limitation
  - Cross-system session sharing
  - Sliding expiration (8 hours)
  - Automatic token refresh

Technical Stack:
Backend:
- FastAPI + SQLAlchemy
- PostgreSQL 16 (10.1.0.20:5433)
- Keycloak Admin API integration
- Docker Mailserver integration (SSH)
- Alembic migrations

Frontend:
- Next.js 14 (App Router)
- NextAuth 4 with Keycloak Provider
- Redis session storage (ioredis)
- Tailwind CSS

Infrastructure:
- Redis 7 (10.1.0.254:6379) - Session + Cache
- Keycloak 26.1.0 (auth.lab.taipei)
- Docker Mailserver (10.1.0.254)

Architecture Highlights:
- Session管理由 Keycloak + Redis 統一控制
- 支援多系統 (HR/WebMail/Calendar/Drive/Office) 共享 session
- Token 自動刷新,異質服務整合
- 未來可無縫遷移到雲端

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

START_BACKEND.bat

@@ -0,0 +1,51 @@
+@echo off
+REM ============================================================================
+REM HR Portal Backend Starting...
+REM ============================================================================
+
+echo ============================================================
+echo HR Portal Backend Starting...
+echo ============================================================
+echo.
+
+REM Check port 10181
+netstat -ano | findstr ":10181" | findstr "LISTENING" >nul
+if %errorlevel% == 0 (
+    echo [ERROR] Port 10181 is already in use!
+    echo.
+    echo Please stop the process first:
+    netstat -ano | findstr ":10181" | findstr "LISTENING"
+    echo.
+    pause
+    exit /b 1
+)
+
+REM Change to backend directory
+cd /d "%~dp0backend"
+
+REM Check and activate virtual environment
+if exist "venv_py311\Scripts\activate.bat" (
+    echo [INFO] Activating virtual environment: venv_py311
+    venv_py311\Scripts\activate.bat && goto :run_server
+) else if exist "venv311\Scripts\activate.bat" (
+    echo [INFO] Activating virtual environment: venv311
+    venv311\Scripts\activate.bat && goto :run_server
+) else (
+    echo [ERROR] Virtual environment not found!
+    echo Please create venv: python -m venv venv_py311
+    pause
+    exit /b 1
+)
+
+:run_server
+echo [INFO] Starting FastAPI application...
+echo [INFO] Backend API: http://localhost:10181
+echo [INFO] API Docs: http://localhost:10181/docs
+echo [INFO] ReDoc: http://localhost:10181/redoc
+echo.
+echo Press Ctrl+C to stop
+echo ============================================================
+echo.
+
+REM Start uvicorn
+venv_py311\Scripts\python.exe -m uvicorn app.main:app --host 0.0.0.0 --port 10181 --reload