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/base.py

@@ -0,0 +1,49 @@
+"""
+基礎 Schema 類別
+"""
+from datetime import datetime
+from pydantic import BaseModel, ConfigDict
+
+
+class BaseSchema(BaseModel):
+    """基礎 Schema"""
+
+    model_config = ConfigDict(
+        from_attributes=True,  # 支援從 ORM 模型轉換
+        use_enum_values=True,   # 使用 Enum 的值
+    )
+
+
+class TimestampSchema(BaseSchema):
+    """帶時間戳的 Schema"""
+
+    created_at: datetime
+    updated_at: datetime
+
+
+class PaginationParams(BaseModel):
+    """分頁參數"""
+
+    page: int = 1
+    page_size: int = 20
+
+    model_config = ConfigDict(
+        json_schema_extra={
+            "example": {
+                "page": 1,
+                "page_size": 20
+            }
+        }
+    )
+
+
+class PaginatedResponse(BaseModel):
+    """分頁響應"""
+
+    total: int
+    page: int
+    page_size: int
+    total_pages: int
+    items: list
+
+    model_config = ConfigDict(from_attributes=True)