feat: add admin UI frontend and complete backend APIs

- Add Vue 3 frontend with Element Plus
- Implement login, dashboard, tenant management
- Add app configuration, logs viewer, stats pages
- Add user management for admins
- Update Drone CI to build and deploy frontend
- Frontend ports: 3001 (test), 4001 (prod)

backend/app/models/user.py

@@ -0,0 +1,19 @@
+"""用户模型"""
+from datetime import datetime
+from sqlalchemy import Column, BigInteger, String, Enum, TIMESTAMP, SmallInteger
+from ..database import Base
+
+
+class User(Base):
+    """用户表"""
+    __tablename__ = "platform_users"
+    
+    id = Column(BigInteger, primary_key=True, autoincrement=True)
+    username = Column(String(50), unique=True, nullable=False)
+    password_hash = Column(String(255), nullable=False)
+    nickname = Column(String(100))
+    role = Column(Enum('admin', 'operator', 'viewer'), default='viewer')
+    status = Column(SmallInteger, default=1)  # 1=启用, 0=禁用
+    last_login_at = Column(TIMESTAMP, nullable=True)
+    created_at = Column(TIMESTAMP, default=datetime.now)
+    updated_at = Column(TIMESTAMP, default=datetime.now, onupdate=datetime.now)