When plan-phase invokes discuss-phase as a nested Skill call,
AskUserQuestion calls auto-resolve with empty answers — the user never
sees the question UI. This is a Claude Code runtime bug with nested
subcontexts.
Made the 'Run discuss-phase first' path explicitly exit the workflow
with a display message instead of risking nested invocation:
- Added explicit warning: do NOT invoke as nested Skill/Task
- Show the command for user to run as top-level
- Exit the plan-phase workflow immediately
Fixes#1009