Simplify return home heuristics now that we have comprehensive travel data

Remove complex country-based return home assumptions since we now track actual train and ferry travel back to the UK. The system can rely on real travel data rather than heuristics.

- Remove NEARBY_BALKAN_COUNTRIES constant
- Remove geographic assumptions about returning home after trips
- Keep only UK trip ending logic (if trip ends in UK, you're home)

With complete train/ferry tracking, actual return travel is captured rather than inferred.

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

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

agenda/busy.py

@@ -11,20 +11,6 @@ from . import events_yaml, get_country, travel
 from .event import Event
 from .types import StrDict, Trip
 
-NEARBY_BALKAN_COUNTRIES = {
-    "GR",
-    "AL",
-    "XK",
-    "HR",
-    "SI",
-    "MK",
-    "BA",
-    "ME",
-    "RS",
-    "BG",
-    "RO",
-}
-
 
 def busy_event(e: Event) -> bool:
     """Busy."""
@@ -522,19 +508,6 @@ def _check_return_home_heuristic(
                 if hasattr(final_country, "alpha_2") and final_country.alpha_2 == "GB":
                     return (None, get_country("gb"))
 
-                # For short trips to nearby countries or international trips
-                # (ended >=1 day ago), assume returned home if no subsequent travel data
-                if days_since_trip >= 1 and (
-                    # European countries (close by rail/ferry)
-                    final_alpha_2 in {"BE", "NL", "FR", "DE", "CH", "AT", "IT", "ES"}
-                    # Nearby Balkan countries
-                    or final_alpha_2 in NEARBY_BALKAN_COUNTRIES
-                    # International trips (assume return home after trip ends)
-                    or final_alpha_2
-                    in {"US", "CA", "IN", "JP", "CN", "AU", "NZ", "BR", "AR", "ZA"}
-                ):
-                    return (None, get_country("gb"))
-
     return None