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>

backend/src/app/api/pokemon.py

@@ -256,19 +256,25 @@ async def delete_pokemon(
     response_model=list[RouteEncounterDetailResponse],
 )
 async def list_route_encounters(
-    route_id: int, session: AsyncSession = Depends(get_session)
+    route_id: int,
+    game_id: int | None = Query(None),
+    session: AsyncSession = Depends(get_session),
 ):
     # Verify route exists
     route = await session.get(Route, route_id)
     if route is None:
         raise HTTPException(status_code=404, detail="Route not found")
 
-    result = await session.execute(
+    query = (
         select(RouteEncounter)
         .where(RouteEncounter.route_id == route_id)
         .options(joinedload(RouteEncounter.pokemon))
         .order_by(RouteEncounter.encounter_rate.desc())
     )
+    if game_id is not None:
+        query = query.where(RouteEncounter.game_id == game_id)
+
+    result = await session.execute(query)
     return result.scalars().unique().all()