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/delete_keycloak_user.py

@@ -0,0 +1,49 @@
+"""
+刪除 Keycloak 用戶
+"""
+import sys
+sys.path.insert(0, '.')
+
+from app.services.keycloak_service import KeycloakService
+
+# 初始化 Keycloak 服務
+keycloak = KeycloakService()
+
+if len(sys.argv) < 2:
+    print("Usage: python delete_keycloak_user.py <user_id_or_username>")
+    sys.exit(1)
+
+user_identifier = sys.argv[1]
+
+print(f"=== Deleting Keycloak User ===\n")
+print(f"Identifier: {user_identifier}\n")
+
+try:
+    # 檢查是否為 UUID (user_id) 或 username
+    if '-' in user_identifier and len(user_identifier) == 36:
+        # 是 UUID,直接刪除
+        user_id = user_identifier
+    else:
+        # 是 username,先查詢 user_id
+        user = keycloak.get_user_by_username(user_identifier)
+        if not user:
+            print(f"ERROR: User '{user_identifier}' not found")
+            sys.exit(1)
+        user_id = user['id']
+        print(f"Found user: {user['username']} (Email: {user['email']})")
+        print(f"User ID: {user_id}\n")
+
+    # 刪除用戶
+    success = keycloak.delete_user(user_id)
+
+    if success:
+        print("\nSUCCESS: User deleted successfully")
+    else:
+        print("\nERROR: Failed to delete user")
+        sys.exit(1)
+
+except Exception as e:
+    print(f"ERROR: {e}")
+    import traceback
+    traceback.print_exc()
+    sys.exit(1)