fix: browse page timestamps show UTC instead of user local time (#482)

* fix: browse page timestamps show UTC instead of user local time

Closes #474

* fix: tests

server/reflector/views/transcripts.py

@@ -1,4 +1,4 @@
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from typing import Annotated, Literal, Optional
 
 import reflector.auth as auth
@@ -6,7 +6,7 @@ from fastapi import APIRouter, Depends, HTTPException
 from fastapi_pagination import Page
 from fastapi_pagination.ext.databases import paginate
 from jose import jwt
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, field_serializer
 from reflector.db.meetings import meetings_controller
 from reflector.db.migrate_user import migrate_user
 from reflector.db.rooms import rooms_controller
@@ -61,6 +61,13 @@ class GetTranscriptMinimal(BaseModel):
     target_language: str | None
     reviewed: bool
     meeting_id: str | None
+
+    @field_serializer("created_at", when_used="json")
+    def serialize_datetime(self, dt: datetime) -> str:
+        if dt.tzinfo is None:
+            dt = dt.replace(tzinfo=timezone.utc)
+        return dt.isoformat()
+
     source_kind: SourceKind
     room_id: str | None = None
     room_name: str | None = None