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/network_drive.py

@@ -0,0 +1,68 @@
+"""
+網路硬碟 Model
+一個員工對應一個 NAS 帳號
+"""
+from datetime import datetime
+from sqlalchemy import Column, Integer, String, Boolean, DateTime, ForeignKey, UniqueConstraint
+from sqlalchemy.orm import relationship
+
+from app.db.base import Base
+
+
+class NetworkDrive(Base):
+    """網路硬碟表"""
+
+    __tablename__ = "tenant_network_drives"
+    __table_args__ = (
+        UniqueConstraint("employee_id", name="uq_network_drive_employee"),
+    )
+
+    id = Column(Integer, primary_key=True, index=True)
+    employee_id = Column(Integer, ForeignKey("tenant_employees.id", ondelete="CASCADE"), nullable=False, unique=True, index=True)
+
+    # 一個員工只有一個 NAS 帳號
+    drive_name = Column(String(100), unique=True, nullable=False, comment="NAS 帳號名稱 (與 username_base 相同)")
+    quota_gb = Column(Integer, nullable=False, comment="配額 (GB),取所有身份中的最高職級")
+
+    # 訪問路徑
+    webdav_url = Column(String(255), comment="WebDAV 路徑")
+    smb_url = Column(String(255), comment="SMB 路徑")
+
+    # 通用欄位
+    is_active = Column(Boolean, default=True, nullable=False, comment="是否啟用")
+    edit_by = Column(String(100), nullable=True, comment="最後編輯者")
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False, comment="建立時間")
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow, nullable=False, comment="更新時間")
+
+    # 關聯
+    employee = relationship("Employee", back_populates="network_drive")
+
+    def __repr__(self):
+        return f"<NetworkDrive {self.drive_name} - {self.quota_gb}GB>"
+
+    @property
+    def webdav_path(self) -> str:
+        """WebDAV 完整路徑"""
+        return self.webdav_url or f"https://nas.lab.taipei/webdav/{self.drive_name}"
+
+    @property
+    def smb_path(self) -> str:
+        """SMB 完整路徑"""
+        return self.smb_url or f"\\\\10.1.0.30\\{self.drive_name}"
+
+    def update_quota_from_job_level(self, job_level: str) -> None:
+        """根據職級更新配額"""
+        from app.core.config import settings
+
+        quota_mapping = {
+            "Junior": settings.NAS_QUOTA_JUNIOR,
+            "Mid": settings.NAS_QUOTA_MID,
+            "Senior": settings.NAS_QUOTA_SENIOR,
+            "Manager": settings.NAS_QUOTA_MANAGER,
+        }
+
+        new_quota = quota_mapping.get(job_level, settings.NAS_QUOTA_JUNIOR)
+
+        # 只在配額增加時更新 (不降低配額)
+        if new_quota > self.quota_gb:
+            self.quota_gb = new_quota