fix: standardize UTC timestamp handling

app/models.py

@@ -1,11 +1,10 @@
 from __future__ import annotations
 
-from datetime import datetime
-
 from flask_login import UserMixin
 from werkzeug.security import check_password_hash, generate_password_hash
 
 from .extensions import db
+from .time_utils import utc_now
 
 
 class User(UserMixin, db.Model):
@@ -15,7 +14,7 @@ class User(UserMixin, db.Model):
     username = db.Column(db.String(100), unique=True, nullable=False)
     password_hash = db.Column(db.String(255), nullable=False)
     is_admin = db.Column(db.Boolean, default=False, nullable=False)
-    created_at = db.Column(db.DateTime, default=datetime.utcnow)
+    created_at = db.Column(db.DateTime, default=utc_now)
 
     def set_password(self, password: str) -> None:
         self.password_hash = generate_password_hash(password)
@@ -33,7 +32,7 @@ class PasswordResetToken(db.Model):
     token_hash = db.Column(db.String(64), unique=True, nullable=False, index=True)
     expires_at = db.Column(db.DateTime, nullable=False)
     used_at = db.Column(db.DateTime)
-    created_at = db.Column(db.DateTime, default=datetime.utcnow, nullable=False)
+    created_at = db.Column(db.DateTime, default=utc_now, nullable=False)
 
     user = db.relationship(
         "User",
@@ -52,7 +51,7 @@ class UploadRecord(db.Model):
     saved_path = db.Column(db.String(500), nullable=False)
     prediction_path = db.Column(db.String(500), nullable=False)
     image_path = db.Column(db.String(500), nullable=False)
-    upload_time = db.Column(db.DateTime, default=datetime.utcnow)
+    upload_time = db.Column(db.DateTime, default=utc_now)
 
     user = db.relationship("User", backref=db.backref("uploads", lazy=True))
 
@@ -63,7 +62,7 @@ class AppSetting(db.Model):
     id = db.Column(db.Integer, primary_key=True)
     key = db.Column(db.String(100), unique=True, nullable=False)
     value = db.Column(db.String(255), nullable=False)
-    updated_at = db.Column(db.DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    updated_at = db.Column(db.DateTime, default=utc_now, onupdate=utc_now)
 
     @classmethod
     def get_bool(cls, key: str, default: bool = False) -> bool: