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/payment.py

@@ -0,0 +1,51 @@
+"""
+付款記錄 Model
+記錄所有付款交易
+"""
+from datetime import datetime
+from sqlalchemy import Column, Integer, String, DateTime, Numeric, ForeignKey, Text
+from sqlalchemy.orm import relationship
+import enum
+
+from app.db.base import Base
+
+
+class PaymentStatus(str, enum.Enum):
+    """付款狀態"""
+    SUCCESS = "success"       # 成功
+    FAILED = "failed"         # 失敗
+    PENDING = "pending"       # 處理中
+    REFUNDED = "refunded"     # 已退款
+
+
+class Payment(Base):
+    """付款記錄表"""
+
+    __tablename__ = "payments"
+
+    id = Column(Integer, primary_key=True, index=True)
+    invoice_id = Column(Integer, ForeignKey("invoices.id", ondelete="CASCADE"), nullable=False, index=True)
+    tenant_id = Column(Integer, ForeignKey("organizes.id", ondelete="CASCADE"), nullable=False, index=True)
+
+    # 付款資訊
+    amount = Column(Numeric(10, 2), nullable=False, comment="付款金額")
+    payment_method = Column(String(20), nullable=False, comment="付款方式 (credit_card/wire_transfer/cash)")
+    transaction_id = Column(String(100), nullable=True, comment="金流交易編號")
+    status = Column(String(20), default=PaymentStatus.PENDING, nullable=False, comment="狀態")
+
+    # 時間記錄
+    paid_at = Column(DateTime, default=datetime.utcnow, nullable=False, comment="付款時間")
+
+    # 備註
+    notes = Column(Text, nullable=True, comment="備註")
+
+    # 關聯
+    invoice = relationship("Invoice", back_populates="payments")
+
+    def __repr__(self):
+        return f"<Payment NT$ {self.amount} - {self.status}>"
+
+    @property
+    def is_success(self) -> bool:
+        """是否付款成功"""
+        return self.status == PaymentStatus.SUCCESS