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>

frontend/services/business-units.ts

@@ -0,0 +1,47 @@
+/**
+ * 事業單位管理 API 服務
+ */
+import { apiClient } from '@/lib/api-client'
+import type { BusinessUnit, PaginatedResponse } from '@/types'
+
+export const businessUnitsService = {
+  /**
+   * 取得事業單位列表
+   */
+  getBusinessUnits: async (params?: {
+    page?: number
+    page_size?: number
+    department_id?: string
+    status?: string
+  }): Promise<PaginatedResponse<BusinessUnit>> => {
+    return apiClient.get('/business-units', { params })
+  },
+
+  /**
+   * 取得單一事業單位詳情
+   */
+  getBusinessUnit: async (id: string): Promise<BusinessUnit> => {
+    return apiClient.get(`/business-units/${id}`)
+  },
+
+  /**
+   * 建立事業單位
+   */
+  createBusinessUnit: async (data: Partial<BusinessUnit>): Promise<BusinessUnit> => {
+    return apiClient.post('/business-units', data)
+  },
+
+  /**
+   * 更新事業單位資料
+   */
+  updateBusinessUnit: async (id: string, data: Partial<BusinessUnit>): Promise<BusinessUnit> => {
+    return apiClient.put(`/business-units/${id}`, data)
+  },
+
+  /**
+   * 刪除事業單位
+   */
+  deleteBusinessUnit: async (id: string): Promise<void> => {
+    return apiClient.delete(`/business-units/${id}`)
+  },
+}