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/hooks/useGames.ts

@@ -23,10 +23,10 @@ export function useGameRoutes(gameId: number | null) {
   })
 }
 
-export function useRoutePokemon(routeId: number | null) {
+export function useRoutePokemon(routeId: number | null, gameId?: number) {
   return useQuery({
-    queryKey: ['routes', routeId, 'pokemon'],
-    queryFn: () => getRoutePokemon(routeId!),
+    queryKey: ['routes', routeId, 'pokemon', gameId],
+    queryFn: () => getRoutePokemon(routeId!, gameId),
     enabled: routeId !== null,
   })
 }