When a recipe defines sub_recipes, the summon extension is now automatically
added to the extensions list. This ensures the delegate tool is available
without requiring users to manually specify the summon extension.
Changes:
- Add ensure_summon_for_subrecipes() helper in Recipe that auto-injects
the summon platform extension when sub_recipes are present
- Update test assertions to expect summon in extension list
- Update test script to look for 'delegate' instead of 'subagent'
Tyler Longwell