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/app/api/v1/router.py

@@ -0,0 +1,144 @@
+"""
+API v1 主路由
+"""
+from fastapi import APIRouter
+
+from app.api.v1 import (
+    auth,
+    tenants,
+    employees,
+    departments,
+    department_members,
+    roles,
+    # identities,  # Removed: EmployeeIdentity and BusinessUnit models have been deleted
+    network_drives,
+    audit_logs,
+    email_accounts,
+    permissions,
+    lifecycle,
+    personal_service_settings,
+    emp_onboarding,
+    system_functions,
+)
+from app.api.v1.endpoints import installation, installation_phases
+
+api_router = APIRouter()
+
+# 認證
+api_router.include_router(
+    auth.router,
+    prefix="/auth",
+    tags=["Authentication"]
+)
+
+# 租戶管理 (多租戶核心)
+api_router.include_router(
+    tenants.router,
+    prefix="/tenants",
+    tags=["Tenants"]
+)
+
+# 員工管理
+api_router.include_router(
+    employees.router,
+    prefix="/employees",
+    tags=["Employees"]
+)
+
+# 部門管理 (統一樹狀結構，取代原 business-units)
+api_router.include_router(
+    departments.router,
+    prefix="/departments",
+    tags=["Departments"]
+)
+
+# 部門成員管理 (員工多部門歸屬)
+api_router.include_router(
+    department_members.router,
+    prefix="/department-members",
+    tags=["Department Members"]
+)
+
+# 角色管理 (RBAC)
+api_router.include_router(
+    roles.router,
+    prefix="/roles",
+    tags=["Roles & RBAC"]
+)
+
+# 身份管理 (已廢棄 API，底層 model 已刪除)
+# api_router.include_router(
+#     identities.router,
+#     prefix="/identities",
+#     tags=["Employee Identities (Deprecated)"]
+# )
+
+# 網路硬碟管理
+api_router.include_router(
+    network_drives.router,
+    prefix="/network-drives",
+    tags=["Network Drives"]
+)
+
+# 審計日誌
+api_router.include_router(
+    audit_logs.router,
+    prefix="/audit-logs",
+    tags=["Audit Logs"]
+)
+
+# 郵件帳號管理
+api_router.include_router(
+    email_accounts.router,
+    prefix="/email-accounts",
+    tags=["Email Accounts"]
+)
+
+# 系統權限管理
+api_router.include_router(
+    permissions.router,
+    prefix="/permissions",
+    tags=["Permissions"]
+)
+
+# 員工生命週期管理
+api_router.include_router(
+    lifecycle.router,
+    prefix="",
+    tags=["Employee Lifecycle"]
+)
+
+# 個人化服務設定管理
+api_router.include_router(
+    personal_service_settings.router,
+    prefix="/personal-services",
+    tags=["Personal Service Settings"]
+)
+
+# 員工到職/離職流程 (v3.1 多租戶架構)
+api_router.include_router(
+    emp_onboarding.router,
+    prefix="/emp-lifecycle",
+    tags=["Employee Onboarding (v3.1)"]
+)
+
+# 系統初始化與健康檢查
+api_router.include_router(
+    installation.router,
+    prefix="/installation",
+    tags=["Installation & Health Check"]
+)
+
+# 系統階段轉換（Initialization/Operational/Transition）
+api_router.include_router(
+    installation_phases.router,
+    prefix="/installation",
+    tags=["System Phase Management"]
+)
+
+# 系統功能管理
+api_router.include_router(
+    system_functions.router,
+    prefix="/system-functions",
+    tags=["System Functions"]
+)