fix: standardize UTC timestamp handling

app/time_utils.py

@@ -5,6 +5,15 @@ from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
 
 
 DEFAULT_TIMEZONE = "Asia/Shanghai"
+DATETIME_DISPLAY_FORMAT = "%Y-%m-%d %H:%M:%S"
+
+
+def utc_now() -> datetime:
+    return datetime.now(timezone.utc).replace(tzinfo=None)
+
+
+def current_year_for_timezone(timezone_name: str | None) -> int:
+    return datetime.now(timezone.utc).astimezone(timezone_for_name(timezone_name)).year
 
 
 def timezone_for_name(name: str | None) -> ZoneInfo:
@@ -19,4 +28,4 @@ def format_datetime_for_timezone(value: datetime | None, timezone_name: str | No
         return "-"
     if value.tzinfo is None:
         value = value.replace(tzinfo=timezone.utc)
-    return value.astimezone(timezone_for_name(timezone_name)).strftime("%Y-%m-%d %H:%M:%S")
+    return value.astimezone(timezone_for_name(timezone_name)).strftime(DATETIME_DISPLAY_FORMAT)