fix(mobile): report markdown link open failures

[fe-franco]

Resolves #5839

What Changed

ThreadFeed.tsx routes all three markdown link presses through
tryOpenExternalUrl with the existing markdown-link target. The now unused
Linking import goes away. Four lines change, and no behavior changes on a
successful tap.

-        void Linking.openURL(props.href);
+        void tryOpenExternalUrl(props.href, "markdown-link");

Why

The three call sites called Linking.openURL directly:

// :274 MarkdownExternalLink, :604 link renderer, :1406 onMarkdownLinkPress
void Linking.openURL(props.href);

Linking.openURL rejects when the device has no handler for the URL. The void
operator discards that rejection, so a failed tap produced no log line.

tryOpenExternalUrl exists for this case and already declares a
markdown-link target. FileMarkdownPreview.tsx uses it on lines 60 and 191.
The thread feed was the only markdown renderer that stayed silent, so this
makes the two agree.

UI Changes

None. The change only adds error reporting on the failure path.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Verification

• vp run --filter @t3tools/mobile typecheck passes.
• vp run --filter @t3tools/mobile test passes, 620 tests in 100 files.
• vp lint --report-unused-disable-directives reports one pre-existing warning
  in apps/web/src/components/settings/ThemeEditorPanel.tsx, untouched here.
• vp fmt --check passes.
• Rebased onto 1a003e383.

Written by Claude Opus 5 in Claude Code.

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on this repository. Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 067fcf25-8658-429a-b7c1-39f1fc337963

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[macroscopeapp]

Approvability

Verdict: Approved 2f8f5cd

This change wraps existing Linking.openURL calls with a helper that adds error handling and structured logging. The core behavior remains unchanged—failures that previously threw are now caught and reported. Low-risk error handling improvement.

^{You can customize Macroscope's approvability policy. Learn more.}

[juliusmarminge]

Closing as superseded by #5872, which has merged and covers this change on the current architecture. Thanks for the contribution.