Add version groups to share routes and boss battles across games

Routes and boss battles now belong to a version_group instead of
individual games, so paired versions (e.g. Red/Blue, Gold/Silver)
share the same route structure and boss battles. Route encounters
gain a game_id column to support game-specific encounter tables
within a shared route. Includes migration, updated seeds, API
changes, and frontend type updates.

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

frontend/src/pages/admin/AdminRouteDetail.tsx

@@ -21,7 +21,7 @@ export function AdminRouteDetail() {
   const rId = Number(routeId)
 
   const { data: game } = useGame(gId)
-  const { data: encounters = [], isLoading } = useRoutePokemon(rId)
+  const { data: encounters = [], isLoading } = useRoutePokemon(rId, gId)
 
   const addEncounter = useAddRouteEncounter(rId)
   const updateEncounter = useUpdateRouteEncounter(rId)
@@ -114,7 +114,7 @@ export function AdminRouteDetail() {
       {showCreate && (
         <RouteEncounterFormModal
           onSubmit={(data) =>
-            addEncounter.mutate(data as CreateRouteEncounterInput, {
+            addEncounter.mutate({ ...data, gameId: gId } as CreateRouteEncounterInput, {
               onSuccess: () => setShowCreate(false),
             })
           }