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/schemas/script_builder.py

@@ -82,3 +82,5 @@ class SaveToLibraryRequest(BaseModel):
     description: str | None = None
     category_id: UUID | None = None
     share_with_team: bool = False
+    script_body: str | None = None
+    parameters_schema: dict | None = None