Parse OpenScale datetime from milliseconds to UTC datetime

Convert timestamp from milliseconds since Unix epoch to proper datetime object with UTC timezone.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

personal_data/fetchers/openscale.py

@@ -5,6 +5,7 @@ OpenScale is an open-source weight tracking app for Android.
 """
 
 import dataclasses
+import datetime
 import sqlite3
 from pathlib import Path
 
@@ -39,4 +40,6 @@ class OpenScale(Scraper):
             """)
 
             for row in cursor.fetchall():
-                yield {'datetime': row['datetime'], 'weight': row['weight']}
+                timestamp_ms = row['datetime']
+                dt = datetime.datetime.fromtimestamp(timestamp_ms / 1000, tz=datetime.timezone.utc)
+                yield {'datetime': dt, 'weight': row['weight']}