hoàn thành chức năng hiện username annotation của từng user

backend/app/schemas.py

@@ -55,6 +55,18 @@ class UserRoleUpdate(BaseModel):
     role: UserRole
 
 
+class ChangePassword(BaseModel):
+    current_password: str
+    new_password: str
+
+    @field_validator("new_password")
+    @classmethod
+    def password_strength(cls, v: str) -> str:
+        if len(v) < 8:
+            raise ValueError("Password must be at least 8 characters.")
+        return v
+
+
 class TokenPayload(BaseModel):
     sub: int   # user id
     exp: int