fix: use platform llm grants for builder

agent_builder/builder.py

@@ -27,8 +27,9 @@ class BuilderContext:
     project_prefix: str | None = None
     workspace: Any | None = None
     grant_token: str | None = None
-    # Optional caller-provided LLM creds (when the outer platform Card
-    # declares llm_provisioning=caller_provided). Falls back to settings.
+    # LLM creds forwarded by the orchestrator according to this agent's Card.
+    # The builder itself uses platform grants; generated agents usually use
+    # caller-provided creds. Falls back to settings for local development.
     llm_base_url: str | None = None
     llm_api_key: str | None = None
     llm_model: str | None = None