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/api/games.py

@@ -15,6 +15,7 @@ from app.schemas.game import (
     RouteReorderRequest,
     RouteResponse,
     RouteUpdate,
+    RouteWithChildrenResponse,
 )
 
 router = APIRouter()
@@ -42,10 +43,21 @@ async def get_game(game_id: int, session: AsyncSession = Depends(get_session)):
     return game
 
 
-@router.get("/{game_id}/routes", response_model=list[RouteResponse])
+@router.get(
+    "/{game_id}/routes",
+    response_model=list[RouteWithChildrenResponse] | list[RouteResponse],
+)
 async def list_game_routes(
-    game_id: int, session: AsyncSession = Depends(get_session)
+    game_id: int,
+    flat: bool = False,
+    session: AsyncSession = Depends(get_session),
 ):
+    """
+    List routes for a game.
+
+    By default, returns a hierarchical structure with top-level routes containing
+    nested children. Use `flat=True` to get a flat list of all routes.
+    """
     # Verify game exists
     game = await session.get(Game, game_id)
     if game is None:
@@ -56,7 +68,36 @@ async def list_game_routes(
         .where(Route.game_id == game_id)
         .order_by(Route.order)
     )
-    return result.scalars().all()
+    all_routes = result.scalars().all()
+
+    if flat:
+        return all_routes
+
+    # Build hierarchical structure
+    # Group children by parent_route_id
+    children_by_parent: dict[int, list[Route]] = {}
+    top_level_routes: list[Route] = []
+
+    for route in all_routes:
+        if route.parent_route_id is None:
+            top_level_routes.append(route)
+        else:
+            children_by_parent.setdefault(route.parent_route_id, []).append(route)
+
+    # Build response with nested children
+    response = []
+    for route in top_level_routes:
+        route_dict = {
+            "id": route.id,
+            "name": route.name,
+            "game_id": route.game_id,
+            "order": route.order,
+            "parent_route_id": route.parent_route_id,
+            "children": children_by_parent.get(route.id, []),
+        }
+        response.append(route_dict)
+
+    return response
 
 
 # --- Admin endpoints ---