Add location tracking to weekend page

Weekend page now shows specific location (city and country) for each
Saturday and Sunday based on travel history:

- Analyzes flight arrivals and accommodation check-ins to determine exact location
- Shows "home" when at Bristol, UK
- Shows "City, 🏴 Country" format when traveling
- Handles multi-location trips by finding most recent travel within trip period
- Optimized to parse YAML files once instead of per-date lookup

Closes #191

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

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

web_view.py

@@ -258,7 +258,7 @@ async def weekends() -> str:
 
     trip_list = agenda.trip.build_trip_list()
     busy_events = agenda.busy.get_busy_events(start, app.config, trip_list)
-    weekends = agenda.busy.weekends(start, busy_events)
+    weekends = agenda.busy.weekends(start, busy_events, trip_list, app.config["PERSONAL_DATA"])
     return flask.render_template(
         "weekends.html",
         items=weekends,