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/schemas/game.py

@@ -7,6 +7,7 @@ class RouteResponse(CamelModel):
     game_id: int
     order: int
     parent_route_id: int | None = None
+    pinwheel_zone: int | None = None
     encounter_methods: list[str] = []
 
 
@@ -56,12 +57,14 @@ class RouteCreate(CamelModel):
     name: str
     order: int
     parent_route_id: int | None = None
+    pinwheel_zone: int | None = None
 
 
 class RouteUpdate(CamelModel):
     name: str | None = None
     order: int | None = None
     parent_route_id: int | None = None
+    pinwheel_zone: int | None = None
 
 
 class RouteReorderItem(CamelModel):