feat(ui): add roadblock reply field to the ROADBLOCK card

A task that reports a roadblock but finishes successfully (Done/WaitingForReview/
Failed/Cancelled) had no way to answer it short of a full reset-and-rerun, losing
the run's context. Adds a reply textbox + Send button to the existing ROADBLOCK
card, modeled on the AskUser question card, that resumes the session via
ContinueTaskAsync with the user's own text. Gated on LatestRunSessionId (disabled
with a hint when there's nothing to resume); failures surface through the footer
error strip instead of a modal.

docs/open.md

@@ -74,6 +74,12 @@ Offene Entscheidungen dazu:
   `WaitingForReview`, and the detail pane's diff/merge card shows the full range of everything the
   run merged to main (via the new `HandlerBaseCommit`/`HandlerHeadCommit` fallback — no
   `WorktreeEntity` is created for this task, so the diff comes from `list.WorkingDir` directly).
+- **Roadblock reply field (2026-08-05)** — build + unit tests all green, but **not visually
+  verified**: on a `Done` (or `WaitingForReview`/`Failed`/`Cancelled`) task with a reported
+  roadblock, the ROADBLOCK card shows a reply textbox + Send button under the roadblock text.
+  Check layout/spacing against the AskUser question card it's modeled on, Enter-to-send, the
+  disabled state + hint text when there's no session ID to resume, and that an override-slot-busy
+  error shows up in the footer log strip (not a modal) with the typed text still in the field.
   Approve should go straight to `Done` with no merge attempt. Design choice: the review range
   lives as two new nullable columns directly on `TaskEntity` (not a phantom `WorktreeEntity` row),
   specifically so `list_worktrees`/the Worktrees overview never see it.