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>

database/docker-compose.yml

@@ -0,0 +1,44 @@
+version: '3.8'
+
+services:
+  postgres:
+    image: postgres:16
+    container_name: hr-portal-db-test
+    environment:
+      POSTGRES_DB: hr_portal
+      POSTGRES_USER: hr_admin
+      POSTGRES_PASSWORD: hr_dev_password_2026
+      POSTGRES_INITDB_ARGS: "--encoding=UTF8 --locale=C"
+    ports:
+      - "5433:5432"  # 使用 5433 避免與其他 PostgreSQL 實例衝突
+    volumes:
+      - hr_portal_db_data:/var/lib/postgresql/data
+    networks:
+      - hr-portal-network
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U hr_admin -d hr_portal"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+
+  pgadmin:
+    image: dpage/pgadmin4:latest
+    container_name: hr-portal-pgadmin
+    environment:
+      PGADMIN_DEFAULT_EMAIL: admin@lab.taipei
+      PGADMIN_DEFAULT_PASSWORD: admin
+      PGADMIN_CONFIG_SERVER_MODE: 'False'
+    ports:
+      - "5050:80"
+    depends_on:
+      - postgres
+    networks:
+      - hr-portal-network
+
+volumes:
+  hr_portal_db_data:
+    driver: local
+
+networks:
+  hr-portal-network:
+    driver: bridge