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>

tests/test_busy.py

@@ -0,0 +1,29 @@
+from datetime import date, datetime
+
+import agenda.trip
+from web_view import app
+
+
+def test_get_location_for_date() -> None:
+    app.config["SERVER_NAME"] = "test"
+    with app.app_context():
+        today = datetime.now().date()
+        start = date(today.year, 1, 1)
+        trips = [
+            t for t in agenda.trip.build_trip_list() if t.start == date(2025, 2, 9)
+        ]
+        assert len(trips) == 1
+
+        data_dir = app.config["PERSONAL_DATA"]
+
+        # Parse YAML files once for the test
+        import agenda.travel as travel
+        bookings = travel.parse_yaml("flights", data_dir)
+        accommodations = travel.parse_yaml("accommodation", data_dir)
+        airports = travel.parse_yaml("airports", data_dir)
+
+        l1 = agenda.busy.get_location_for_date(date(2025, 2, 15), trips, bookings, accommodations, airports)
+        assert l1[0] == "Hackettstown"
+
+        l2 = agenda.busy.get_location_for_date(date(2025, 7, 1), trips, bookings, accommodations, airports)
+        assert l2[0] == "Bristol"