Task page live-row guard UX gaps

Seen on the task page (local stack, desktop 1280 and phone 400) while verifying Task 8084: 1. A Go withheld because the row is waiting on a question shows no reason on screen (hover only); show a one-line reason beside the bar, as the dispatch-block note already does. 2. Crossing the split width remounts the page and loses the "stay on Task" hold from Task 8084: a phone-width resize after a question arrived mid-typing lands on Answer. Keep the hold (or write `?tab=task`) across the remount. 3. "Assigned to" renders an empty box on a row whose assignee is not in the roster; name the stored assignee or say "Unassigned". 4. Cancelling Go's late reset confirm (a row that went running during the save) navigates to the list like Save; consider staying on the page with "Saved; not restarted". Out of scope: the page's visual polish task; anything in Task 8084's shipped behaviour beyond the items above. Done means: - Each item fixed or ruled out with evidence; vitest covers 1, 2 and 4; a live screenshot at desktop and phone width.

Fixed all 4: Go-blocked reason on the action bar, the Task hold survives the split-width remount (?tab=task pin, cleared with the gate), "Unassigned" placeholder, a cancelled late reset stays with "Saved; not restarted". Quick gate green; vitest 2175/2175; visual check at 1280/400 done. PR #6314 queued in the lane. Follow-up draft #8109.