[codex] Polish issue board workflows (#4224)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - Human operators supervise that work through issue lists, issue
detail, comments, inbox groups, markdown references, and
profile/activity surfaces
> - The branch had many small UI fixes that improve the operator loop
but do not need to ship with backend runtime migrations
> - These changes belong together as board workflow polish because they
affect scanning, navigation, issue context, comment state, and markdown
clarity
> - This pull request groups the UI-only slice so it can merge
independently from runtime/backend changes
> - The benefit is a clearer board experience with better issue context,
steadier optimistic updates, and more predictable keyboard navigation

## What Changed

- Improves issue properties, sub-issue actions, blocker chips, and issue
list/detail refresh behavior.
- Adds blocker context above the issue composer and stabilizes
queued/interrupted comment UI state.
- Improves markdown issue/GitHub link rendering and opens external
markdown links in a new tab.
- Adds inbox group keyboard navigation and fold/unfold support.
- Polishes activity/avatar/profile/settings/workspace presentation
details.

## Verification

- `pnpm exec vitest run ui/src/components/IssueProperties.test.tsx
ui/src/components/IssueChatThread.test.tsx
ui/src/components/MarkdownBody.test.tsx ui/src/lib/inbox.test.ts
ui/src/lib/optimistic-issue-comments.test.ts`

## Risks

- Low to medium risk: changes are UI-focused but cover high-traffic
issue and inbox surfaces.
- This branch intentionally does not include the backend runtime changes
from the companion PR; where UI calls newer API filters, unsupported
servers should continue to fail visibly through existing API error
handling.
- Visual screenshots were not captured in this heartbeat; targeted
component/helper tests cover the changed behavior.

> 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 runtime, shell/git tool use
enabled. Exact hosted model build and context window are not exposed in
this Paperclip heartbeat 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
- [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

ui/src/components/MarkdownBody.tsx

@@ -1,5 +1,6 @@
 import { isValidElement, useEffect, useId, useState, type ReactNode } from "react";
 import { useQuery } from "@tanstack/react-query";
+import { Github } from "lucide-react";
 import Markdown, { defaultUrlTransform, type Components, type Options } from "react-markdown";
 import remarkGfm from "remark-gfm";
 import { cn } from "../lib/utils";
@@ -103,6 +104,28 @@ function safeMarkdownUrlTransform(url: string): string {
   return parseMentionChipHref(url) ? url : defaultUrlTransform(url);
 }
 
+function isGitHubUrl(href: string | null | undefined): boolean {
+  if (!href) return false;
+  try {
+    const url = new URL(href);
+    return url.protocol === "https:" && (url.hostname === "github.com" || url.hostname === "www.github.com");
+  } catch {
+    return false;
+  }
+}
+
+function isExternalHttpUrl(href: string | null | undefined): boolean {
+  if (!href) return false;
+  try {
+    const url = new URL(href);
+    if (url.protocol !== "http:" && url.protocol !== "https:") return false;
+    if (typeof window === "undefined") return true;
+    return url.origin !== window.location.origin;
+  } catch {
+    return false;
+  }
+}
+
 function MermaidDiagramBlock({ source, darkMode }: { source: string; darkMode: boolean }) {
   const renderId = useId().replace(/[^a-zA-Z0-9_-]/g, "");
   const [svg, setSvg] = useState<string | null>(null);
@@ -249,8 +272,17 @@ export function MarkdownBody({
           </a>
         );
       }
+      const isGitHubLink = isGitHubUrl(href);
+      const isExternal = isExternalHttpUrl(href);
       return (
-        <a href={href} rel="noreferrer" style={mergeWrapStyle(linkStyle as React.CSSProperties | undefined)}>
+        <a
+          href={href}
+          {...(isExternal
+            ? { target: "_blank", rel: "noopener noreferrer" }
+            : { rel: "noreferrer" })}
+          style={mergeWrapStyle(linkStyle as React.CSSProperties | undefined)}
+        >
+          {isGitHubLink ? <Github aria-hidden="true" className="mr-1 inline h-3.5 w-3.5 align-[-0.125em]" /> : null}
           {linkChildren}
         </a>
       );