Add non-evolution form change support (Rotom, Oricorio, etc.)

Add a "Change Form" button in StatusChangeModal for Pokemon with
alternate forms sharing the same national_dex number. Mirrors the
existing evolution UI pattern, reusing currentPokemonId to track
the active form.

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

backend/src/app/api/pokemon.py

@@ -158,6 +158,22 @@ async def get_pokemon(
     return pokemon
 
 
+@router.get("/pokemon/{pokemon_id}/forms", response_model=list[PokemonResponse])
+async def get_pokemon_forms(
+    pokemon_id: int, session: AsyncSession = Depends(get_session)
+):
+    pokemon = await session.get(Pokemon, pokemon_id)
+    if pokemon is None:
+        raise HTTPException(status_code=404, detail="Pokemon not found")
+
+    result = await session.execute(
+        select(Pokemon)
+        .where(Pokemon.national_dex == pokemon.national_dex, Pokemon.id != pokemon_id)
+        .order_by(Pokemon.pokeapi_id)
+    )
+    return result.scalars().all()
+
+
 @router.get("/pokemon/{pokemon_id}/evolutions", response_model=list[EvolutionResponse])
 async def get_pokemon_evolutions(
     pokemon_id: int,