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/schemas/tenant.py

@@ -0,0 +1,134 @@
+"""
+租戶相關 Pydantic Schemas
+"""
+from datetime import datetime
+from typing import Optional, List
+from pydantic import BaseModel, Field, validator
+
+
+class TenantBase(BaseModel):
+    """租戶基本資料"""
+    code: str = Field(..., min_length=2, max_length=50, description="租戶代碼")
+    name: str = Field(..., min_length=1, max_length=200, description="公司名稱")
+    name_eng: Optional[str] = Field(None, max_length=200, description="公司英文名稱")
+    tax_id: Optional[str] = Field(None, max_length=20, description="統一編號")
+    prefix: str = Field(..., min_length=1, max_length=10, description="員工編號前綴")
+    tel: Optional[str] = Field(None, max_length=50, description="公司電話")
+    add: Optional[str] = Field(None, max_length=500, description="公司地址")
+    url: Optional[str] = Field(None, max_length=200, description="公司網站")
+    plan_id: str = Field(default="starter", description="方案 ID")
+    max_users: int = Field(default=5, ge=1, description="最大用戶數")
+    storage_quota_gb: int = Field(default=100, ge=1, description="總儲存配額 (GB)")
+
+
+class TenantCreateRequest(TenantBase):
+    """建立租戶請求 (Superuser only)"""
+    admin_username: str = Field(..., description="Tenant Admin 帳號")
+    admin_email: str = Field(..., description="Tenant Admin 郵件")
+    admin_name: str = Field(..., description="Tenant Admin 姓名")
+    admin_temp_password: str = Field(..., min_length=8, description="Tenant Admin 臨時密碼")
+
+    @validator('admin_email')
+    def validate_email(cls, v):
+        """驗證郵件格式"""
+        if '@' not in v:
+            raise ValueError('Invalid email format')
+        return v
+
+    @validator('tax_id')
+    def validate_tax_id(cls, v):
+        """驗證統一編號 (台灣 8 位數字)"""
+        if v and (not v.isdigit() or len(v) != 8):
+            raise ValueError('Tax ID must be 8 digits')
+        return v
+
+
+class TenantCreateResponse(BaseModel):
+    """建立租戶回應"""
+    message: str
+    tenant: dict
+    admin_user: dict
+    keycloak_realm: str
+    temporary_password: str  # 返回臨時密碼供管理員記錄
+
+    class Config:
+        from_attributes = True
+
+
+class TenantUpdateRequest(BaseModel):
+    """更新租戶請求"""
+    name: Optional[str] = Field(None, min_length=1, max_length=200)
+    name_eng: Optional[str] = Field(None, max_length=200)
+    tax_id: Optional[str] = Field(None, max_length=20)
+    tel: Optional[str] = Field(None, max_length=50)
+    add: Optional[str] = Field(None, max_length=500)
+    url: Optional[str] = Field(None, max_length=200)
+
+    @validator('tax_id')
+    def validate_tax_id(cls, v):
+        """驗證統一編號"""
+        if v and (not v.isdigit() or len(v) != 8):
+            raise ValueError('Tax ID must be 8 digits')
+        return v
+
+
+class TenantUpdateResponse(BaseModel):
+    """更新租戶回應"""
+    message: str
+    tenant: dict
+
+    class Config:
+        from_attributes = True
+
+
+class TenantResponse(BaseModel):
+    """租戶詳細資訊"""
+    id: int
+    code: str
+    name: str
+    name_eng: Optional[str]
+    tax_id: Optional[str]
+    prefix: str
+    tel: Optional[str]
+    add: Optional[str]
+    url: Optional[str]
+    keycloak_realm: Optional[str]
+    plan_id: str
+    max_users: int
+    storage_quota_gb: int
+    status: str
+    is_sysmana: bool
+    is_active: bool
+    is_initialized: bool
+    initialized_at: Optional[datetime]
+    initialized_by: Optional[str]
+    created_at: datetime
+    updated_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+class InitializationRequest(BaseModel):
+    """租戶初始化請求 (Tenant Admin only)"""
+
+    # Step 1: 公司基本資料 (可修改)
+    company_info: dict = Field(..., description="公司基本資料")
+
+    # Step 2: 部門結構
+    departments: List[dict] = Field(..., description="部門列表")
+
+    # Step 3: 系統角色
+    roles: List[dict] = Field(..., description="角色列表")
+
+    # Step 4: 預設配額與服務
+    default_settings: dict = Field(..., description="預設配額與服務")
+
+
+class InitializationResponse(BaseModel):
+    """初始化完成回應"""
+    message: str
+    summary: dict
+
+    class Config:
+        from_attributes = True