Adds --all to /gsd-discuss-phase so users can skip the AskUserQuestion
area-selection step and jump straight into discussing all gray areas
interactively. Unlike --auto, --all does NOT auto-advance to plan-phase —
it only eliminates the selection friction while keeping full interactive
control over each discussion.
Closes#2188
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
