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/seeds/loader.py

@@ -66,20 +66,54 @@ async def upsert_routes(
     game_id: int,
     routes: list[dict],
 ) -> dict[str, int]:
-    """Upsert route records for a game, return {name: id} mapping."""
+    """Upsert route records for a game, return {name: id} mapping.
+
+    Handles hierarchical routes: routes with 'children' are parent routes,
+    and their children get parent_route_id set accordingly.
+    """
+    # First pass: upsert all parent routes (without parent_route_id)
     for route in routes:
         stmt = insert(Route).values(
             name=route["name"],
             game_id=game_id,
             order=route["order"],
+            parent_route_id=None,  # Parent routes have no parent
         ).on_conflict_do_update(
             constraint="uq_routes_game_name",
-            set_={"order": route["order"]},
+            set_={"order": route["order"], "parent_route_id": None},
         )
         await session.execute(stmt)
 
     await session.flush()
 
+    # Get mapping of parent routes
+    result = await session.execute(
+        select(Route.name, Route.id).where(Route.game_id == game_id)
+    )
+    name_to_id = {row.name: row.id for row in result}
+
+    # Second pass: upsert child routes with parent_route_id
+    for route in routes:
+        children = route.get("children", [])
+        if not children:
+            continue
+
+        parent_id = name_to_id[route["name"]]
+        for child in children:
+            stmt = insert(Route).values(
+                name=child["name"],
+                game_id=game_id,
+                order=child["order"],
+                parent_route_id=parent_id,
+            ).on_conflict_do_update(
+                constraint="uq_routes_game_name",
+                set_={"order": child["order"], "parent_route_id": parent_id},
+            )
+            await session.execute(stmt)
+
+    await session.flush()
+
+    # Return full mapping including children
     result = await session.execute(
         select(Route.name, Route.id).where(Route.game_id == game_id)
     )