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/tests/test_drive_service.py

@@ -0,0 +1,98 @@
+"""
+Drive Service HTTP Client 單元測試 (6.3)
+使用 mock 測試，不需要實際 Drive Service 上線
+"""
+import pytest
+from unittest.mock import patch, MagicMock
+from app.services.drive_service import DriveServiceClient, get_drive_quota_by_job_level
+
+
+class TestGetDriveQuotaByJobLevel:
+    """職級配額對應測試"""
+
+    def test_junior_quota(self):
+        assert get_drive_quota_by_job_level("Junior") == 50
+
+    def test_mid_quota(self):
+        assert get_drive_quota_by_job_level("Mid") == 100
+
+    def test_senior_quota(self):
+        assert get_drive_quota_by_job_level("Senior") == 200
+
+    def test_manager_quota(self):
+        assert get_drive_quota_by_job_level("Manager") == 500
+
+    def test_unknown_level_defaults_to_junior(self):
+        assert get_drive_quota_by_job_level("Unknown") == 50
+
+    def test_none_defaults_to_junior(self):
+        assert get_drive_quota_by_job_level(None) == 50
+
+
+class TestDriveServiceClient:
+    """Drive Service HTTP Client 測試"""
+
+    def setup_method(self):
+        self.client = DriveServiceClient(
+            base_url="https://drive-api.ease.taipei",
+            timeout=5,
+        )
+
+    def test_create_user_service_unavailable(self):
+        """Drive Service 未上線時回傳 warning 結果"""
+        from requests.exceptions import ConnectionError as RequestsConnectionError
+        with patch.object(self.client.session, "post") as mock_post:
+            mock_post.side_effect = RequestsConnectionError("Connection refused")
+            result = self.client.create_user(
+                tenant_id=1,
+                keycloak_user_id="kc-uuid-123",
+                username="test.user",
+                email="test.user@porscheworld.tw",
+                display_name="Test User",
+                quota_gb=100,
+            )
+        assert result["created"] is False
+        assert result["error"] is not None
+        assert "test.user" in str(result)
+
+    def test_create_user_success(self):
+        """Drive Service 正常回應時成功建立"""
+        with patch.object(self.client.session, "post") as mock_post:
+            mock_response = MagicMock()
+            mock_response.status_code = 201
+            mock_response.json.return_value = {
+                "id": 42,
+                "username": "test.user",
+                "quota_gb": 100,
+                "drive_url": "https://drive.ease.taipei/test.user",
+            }
+            mock_post.return_value = mock_response
+
+            result = self.client.create_user(
+                tenant_id=1,
+                keycloak_user_id="kc-uuid-123",
+                username="test.user",
+                email="test.user@porscheworld.tw",
+                display_name="Test User",
+                quota_gb=100,
+            )
+        assert result["created"] is True
+        assert result["error"] is None
+        assert result["quota_gb"] == 100
+
+    def test_get_quota_service_unavailable(self):
+        """Drive Service 未上線時查詢配額回傳 None"""
+        from requests.exceptions import ConnectionError as RequestsConnectionError
+        with patch.object(self.client.session, "get") as mock_get:
+            mock_get.side_effect = RequestsConnectionError("Connection refused")
+            result = self.client.get_quota(drive_user_id=42)
+        assert result is None
+
+    def test_disable_user_service_unavailable(self):
+        """Drive Service 未上線時停用帳號回傳 False"""
+        from requests.exceptions import ConnectionError as RequestsConnectionError
+        with patch.object(self.client.session, "delete") as mock_delete:
+            mock_delete.side_effect = RequestsConnectionError("Connection refused")
+            result = self.client.disable_user(drive_user_id=42)
+        assert result["disabled"] is False
+        assert result["error"] is not None