[codex] Polish inbox nested issue UI (#4959)

## Thinking Path

> - Paperclip orchestrates AI agents through issue lists and
issue-thread interactions
> - The inbox must preserve nested issue visibility and keyboard
navigation as work decomposes into deeper sub-issues
> - Some UI polish issues made nested rows harder to scan and pending
question cancellation less covered
> - The issue list also had a small test indentation regression around
load-more behavior
> - This pull request tightens nested inbox rendering and related
issue-thread/list polish
> - The benefit is a more reliable operator inbox for multi-level work
trees

## What Changed

- Included nested grandchild issues in inbox keyboard navigation and
recursive row rendering.
- Sort parent rows by descendant activity so active subtrees remain
visible.
- Removed extra inbox card background styling in favor of the page
surface.
- Added regression coverage for pending question cancellation.
- Cleaned up the issue-list load-more test indentation.

## Verification

- `pnpm exec vitest run ui/src/lib/inbox.test.ts
ui/src/components/IssueChatThread.test.tsx
ui/src/components/IssuesList.test.tsx`
- Screenshots were not captured in this PR split; the visible flow is
covered by focused component/helper tests and should get browser QA in
the follow-up issue.

## Risks

- Medium risk: nested inbox rendering and keyboard navigation are
user-visible. The changes are localized to inbox grouping/rendering
helpers and covered by targeted tests.

> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.

## Model Used

- OpenAI Codex, GPT-5 coding agent, tool use and local command
execution. Exact context window was not exposed in the runtime.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [ ] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

ui/src/components/IssueThreadInteractionCard.tsx

@@ -807,8 +807,8 @@ function AskUserQuestionsCard({
                   ) : (
                     "Cancel question"
                   )}
-                </Button>
-              ) : null}
+                  </Button>
+                ) : null}
               <Button
                 size="sm"
                 disabled={!onSubmitInteractionAnswers || !canSubmit || working || cancelling}