[codex] Refine markdown issue reference rendering (#4382)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - Task references are a core part of how operators understand issue
relationships across the UI
> - Those references appear both in markdown bodies and in sidebar
relationship panels
> - The rendering had drifted between surfaces, and inline markdown
pills were reading awkwardly inside prose and lists
> - This pull request unifies the underlying issue-reference treatment,
routes issue descriptions through `MarkdownBody`, and switches inline
markdown references to a cleaner text-link presentation
> - The benefit is more consistent issue-reference UX with better
readability in markdown-heavy views

## What Changed

- unified sidebar and markdown issue-reference rendering around the
shared issue-reference components
- routed resting issue descriptions through `MarkdownBody` so
description previews inherit the richer issue-reference treatment
- replaced inline markdown pill chrome with a cleaner inline reference
presentation for prose contexts
- added and updated UI tests for `MarkdownBody` and `InlineEditor`

## Verification

- `pnpm exec vitest run --project @paperclipai/ui
ui/src/components/MarkdownBody.test.tsx
ui/src/components/InlineEditor.test.tsx`

## Risks

- Moderate UI risk: issue-reference rendering now differs intentionally
between inline markdown and relationship sidebars, so regressions would
show up as styling or hover-preview mismatches

> 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-based coding agent with tool use and code execution
in the Codex CLI environment

## 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
- [ ] 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/IssueReferencePill.tsx

@@ -1,3 +1,4 @@
+import type { ReactNode } from "react";
 import type { IssueRelationIssueSummary } from "@paperclipai/shared";
 import { Link } from "@/lib/router";
 import { cn } from "../lib/utils";
@@ -7,11 +8,13 @@ export function IssueReferencePill({
   issue,
   strikethrough,
   className,
+  children,
 }: {
   issue: Pick<IssueRelationIssueSummary, "id" | "identifier" | "title"> &
     Partial<Pick<IssueRelationIssueSummary, "status">>;
   strikethrough?: boolean;
   className?: string;
+  children?: ReactNode;
 }) {
   const issueLabel = issue.identifier ?? issue.title;
   const classNames = cn(
@@ -24,7 +27,7 @@ export function IssueReferencePill({
   const content = (
     <>
       {issue.status ? <StatusIcon status={issue.status} className="h-3 w-3 shrink-0" /> : null}
-      <span>{issue.identifier ?? issue.title}</span>
+      {children !== undefined ? children : <span>{issue.identifier ?? issue.title}</span>}
     </>
   );