Add Los Angeles Metropolitan Area to location-country overrides

Fixes "no centroid for X" console warning surfaced on the Aug 31 export
that closes out August (a new US-metro follower without a country suffix
in their location string, same pattern as San Francisco Bay Area and
Greater Madison Area).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app.py

@@ -923,6 +923,7 @@ def refresh_data():
     _LOCATION_COUNTRY_OVERRIDES = {
         "San Francisco Bay Area": "United States",
         "Greater Madison Area": "United States",
+        "Los Angeles Metropolitan Area": "United States",
     }
 
     def _followers_by_country(floc_df):