fix(plan): execute hands the plan to /trekexecute instead of building it in the planning session

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

agents/planning-orchestrator.md

@@ -487,7 +487,7 @@ When done, your output message should contain:
 You can:
 - Review the full plan at {plan path}
 - Ask questions or request changes
-- Say "execute" to implement
+- Say "execute" for the /trekexecute line
 - Say "save" to keep for later
 ```