Hide outdated review comments in PR timeline

[Copilot]

Outdated review comments (those with position === null) now display as minimal timeline items instead of full comment threads, reducing clutter in the PR overview.

Changes:

• webviews/components/timeline.tsx: Modified CommentThread component to detect outdated comments and render a minimal placeholder showing "This comment was marked as outdated." with a link to GitHub source
• webviews/editorWebview/index.css: Added .outdated-comment styling using VS Code theme variables

Before:

// Full comment thread displayed with "Outdated" badge
<div className="resolved-container">
  <span>{comment.path}</span>
  <span className="outdatedLabel">Outdated</span>
  {/* Full diff and comments shown */}
</div>

After:

// Minimal timeline item for outdated comments
<div className="outdated-comment">
  <span>This comment was marked as outdated.</span>
  <a href={comment.htmlUrl}>View in GitHub</a>
</div>

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Feature request: hidden comments</issue_title> <issue_description>

Comments that are marked as hidden on github are currently still shown:

which on github is shown as

from https://github.com/jorenham/numpy-typing-compat/pull/32

---

So I think that it would help if those comments would also be hidden the VSCode PR interface in the same manner, preferably including the reason for why it's hidden (i.e. the "This comment was marked as outdated." above).</issue_description>

<agent_instructions>Hide outdated comments in the pull request overview. Just show a timeline item and "This comment was marked as outdated", with a link to show the comment in the source.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes microsoft/vscode-pull-request-github#7431

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