feat: accept script_body and parameters_schema in save-to-library flow

Previously save_to_library() hardcoded parameters_schema to empty and
always used session.latest_script. Now accepts optional overrides from
the frontend for parameterized script bodies.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/api/endpoints/script_builder.py

@@ -179,6 +179,8 @@ async def save_to_library(
             share_with_team=data.share_with_team,
             user_id=current_user.id,
             team_id=current_user.team_id,
+            script_body=data.script_body,
+            parameters_schema=data.parameters_schema,
         )
     except ValueError as e:
         raise HTTPException(status_code=400, detail=str(e))