Add hierarchical route grouping for multi-area locations

Locations like Mt. Moon (with 1F, B1F, B2F floors) are now grouped so
only one encounter can be logged per location group, enforcing Nuzlocke
first-encounter rules correctly.

- Add parent_route_id column with self-referential FK to routes table
- Add parent/children relationships on Route model
- Update games API to return hierarchical route structure
- Add validation in encounters API to prevent parent route encounters
  and duplicate encounters within sibling routes (409 conflict)
- Update frontend with collapsible RouteGroup component
- Auto-derive route groups from PokeAPI location/location-area structure
- Regenerate seed data with 70 parent routes and 315 child routes

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/app/schemas/game.py

@@ -6,6 +6,7 @@ class RouteResponse(CamelModel):
     name: str
     game_id: int
     order: int
+    parent_route_id: int | None = None
 
 
 class GameResponse(CamelModel):
@@ -18,6 +19,10 @@ class GameResponse(CamelModel):
     release_year: int | None
 
 
+class RouteWithChildrenResponse(RouteResponse):
+    children: list[RouteResponse] = []
+
+
 class GameDetailResponse(GameResponse):
     routes: list[RouteResponse] = []
 
@@ -46,11 +51,13 @@ class GameUpdate(CamelModel):
 class RouteCreate(CamelModel):
     name: str
     order: int
+    parent_route_id: int | None = None
 
 
 class RouteUpdate(CamelModel):
     name: str | None = None
     order: int | None = None
+    parent_route_id: int | None = None
 
 
 class RouteReorderItem(CamelModel):