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/models/tenant_domain.py

@@ -0,0 +1,119 @@
+"""
+租戶網域 Model
+支援單一租戶使用多個網域 (多品牌/國際化)
+"""
+from datetime import datetime
+from sqlalchemy import Column, Integer, String, Boolean, DateTime, ForeignKey, UniqueConstraint, Index
+from sqlalchemy.orm import relationship
+import enum
+
+from app.db.base import Base
+
+
+class DomainStatus(str, enum.Enum):
+    """網域狀態"""
+    PENDING = "pending"       # 待驗證
+    ACTIVE = "active"         # 啟用中
+    DISABLED = "disabled"     # 已停用
+
+
+class TenantDomain(Base):
+    """租戶網域表 (一個租戶可以有多個網域)"""
+
+    __tablename__ = "tenant_domains"
+    __table_args__ = (
+        # 每個租戶只能有一個主要網域
+        Index("idx_tenant_primary_domain", "tenant_id", unique=True, postgresql_where=Column("is_primary") == True),
+        # 一般索引
+        Index("idx_tenant_domains_tenant", "tenant_id"),
+        Index("idx_tenant_domains_status", "status"),
+    )
+
+    id = Column(Integer, primary_key=True, index=True)
+    tenant_id = Column(Integer, ForeignKey("organizes.id", ondelete="CASCADE"), nullable=False, index=True)
+    domain = Column(String(100), unique=True, nullable=False, index=True, comment="網域名稱 (abc.com.tw)")
+
+    # 網域屬性
+    is_primary = Column(Boolean, default=False, nullable=False, comment="是否為主要網域")
+    status = Column(String(20), default=DomainStatus.PENDING, nullable=False, comment="狀態")
+    verified = Column(Boolean, default=False, nullable=False, comment="DNS 驗證狀態")
+
+    # DNS 驗證
+    verification_token = Column(String(100), nullable=True, comment="驗證 Token")
+    verified_at = Column(DateTime, nullable=True, comment="驗證時間")
+
+    # 服務啟用狀態
+    enable_email = Column(Boolean, default=True, nullable=False, comment="啟用郵件服務")
+    enable_webmail = Column(Boolean, default=True, nullable=False, comment="啟用 WebMail")
+    enable_drive = Column(Boolean, default=True, nullable=False, comment="啟用雲端硬碟")
+
+    # 時間記錄
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow, nullable=False)
+
+    # 關聯
+    tenant = relationship("Tenant", back_populates="domains")
+    email_aliases = relationship(
+        "UserEmailAlias",
+        back_populates="domain",
+        cascade="all, delete-orphan",
+        lazy="dynamic"
+    )
+
+    def __repr__(self):
+        return f"<TenantDomain {self.domain} ({'主要' if self.is_primary else '次要'})>"
+
+    @property
+    def is_verified(self) -> bool:
+        """是否已驗證"""
+        return self.verified and self.status == DomainStatus.ACTIVE
+
+    def generate_dns_records(self) -> list:
+        """生成 DNS 驗證記錄指引"""
+        records = []
+
+        # TXT 記錄 - 網域所有權驗證
+        records.append({
+            "type": "TXT",
+            "name": "@",
+            "value": f"porsche-cloud-verify={self.verification_token}",
+            "purpose": "網域所有權驗證"
+        })
+
+        if self.enable_email:
+            # MX 記錄 - 郵件伺服器
+            records.append({
+                "type": "MX",
+                "name": "@",
+                "value": "mail.porschecloud.tw",
+                "priority": 10,
+                "purpose": "郵件伺服器"
+            })
+
+            # SPF 記錄 - 防止郵件偽造
+            records.append({
+                "type": "TXT",
+                "name": "@",
+                "value": "v=spf1 include:porschecloud.tw ~all",
+                "purpose": "郵件 SPF 記錄"
+            })
+
+        if self.enable_webmail:
+            # CNAME - WebMail
+            records.append({
+                "type": "CNAME",
+                "name": "mail",
+                "value": f"tenant-{self.tenant.tenant_code}.porschecloud.tw",
+                "purpose": "WebMail 訪問"
+            })
+
+        if self.enable_drive:
+            # CNAME - 雲端硬碟
+            records.append({
+                "type": "CNAME",
+                "name": "drive",
+                "value": f"tenant-{self.tenant.tenant_code}.porschecloud.tw",
+                "purpose": "雲端硬碟訪問"
+            })
+
+        return records