Add Pinwheel Clause support for zone-based encounters in route groups

Allows each sub-zone within a route group to have its own independent
encounter when the Pinwheel Clause rule is enabled (default on), instead
of the entire group sharing a single encounter.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/app/seeds/loader.py

@@ -109,9 +109,14 @@ async def upsert_routes(
                 game_id=game_id,
                 order=child["order"],
                 parent_route_id=parent_id,
+                pinwheel_zone=child.get("pinwheel_zone"),
             ).on_conflict_do_update(
                 constraint="uq_routes_game_name",
-                set_={"order": child["order"], "parent_route_id": parent_id},
+                set_={
+                    "order": child["order"],
+                    "parent_route_id": parent_id,
+                    "pinwheel_zone": child.get("pinwheel_zone"),
+                },
             )
             await session.execute(stmt)