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>

backend/Dockerfile

@@ -0,0 +1,59 @@
+# ============================================================================
+# HR Portal Backend Dockerfile
+# FastAPI + Python 3.11 + PostgreSQL
+# ============================================================================
+
+FROM python:3.11-slim as base
+
+# 設定環境變數
+ENV PYTHONUNBUFFERED=1 \
+    PYTHONDONTWRITEBYTECODE=1 \
+    PIP_NO_CACHE_DIR=1 \
+    PIP_DISABLE_PIP_VERSION_CHECK=1
+
+# 設定工作目錄
+WORKDIR /app
+
+# 安裝系統依賴
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    gcc \
+    postgresql-client \
+    && rm -rf /var/lib/apt/lists/*
+
+# ============================================================================
+# Builder Stage - 安裝 Python 依賴
+# ============================================================================
+FROM base as builder
+
+# 複製需求檔案
+COPY requirements.txt .
+
+# 安裝 Python 依賴
+RUN pip install --user --no-warn-script-location -r requirements.txt
+
+# ============================================================================
+# Runtime Stage - 最終映像
+# ============================================================================
+FROM base
+
+# 從 builder 複製已安裝的套件
+COPY --from=builder /root/.local /root/.local
+
+# 確保 scripts 在 PATH 中
+ENV PATH=/root/.local/bin:$PATH
+
+# 複製應用程式碼
+COPY . /app
+
+# 創建日誌目錄
+RUN mkdir -p /app/logs
+
+# 暴露端口
+EXPOSE 8000
+
+# 健康檢查
+HEALTHCHECK --interval=30s --timeout=10s --start-period=40s --retries=3 \
+    CMD python -c "import httpx; httpx.get('http://localhost:8000/health', timeout=5.0)" || exit 1
+
+# 啟動命令
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000", "--workers", "4"]