feat: JWT auth, user management, audit logging system

Co-Authored-By: Claude <noreply@anthropic.com>

backend/app/schemas/auth.py

@@ -0,0 +1,23 @@
+from pydantic import BaseModel
+
+
+class LoginRequest(BaseModel):
+    username: str
+    password: str
+
+
+class RegisterRequest(BaseModel):
+    username: str
+    email: str  # 先用 str，后续升级 EmailStr
+    password: str
+
+
+class TokenResponse(BaseModel):
+    access_token: str
+    token_type: str = "bearer"
+    expires_in: int = 0
+
+
+class ChangePasswordRequest(BaseModel):
+    old_password: str
+    new_password: str

backend/app/schemas/user.py

@@ -0,0 +1,19 @@
+from pydantic import BaseModel, ConfigDict
+from datetime import datetime
+
+
+class UserResponse(BaseModel):
+    id: str
+    username: str
+    email: str
+    role: str
+    is_active: bool
+    is_approved: bool
+    created_at: datetime
+
+    model_config = ConfigDict(from_attributes=True)
+
+
+class UserUpdateRequest(BaseModel):
+    role: str | None = None
+    is_active: bool | None = None