Fix flaky extension installed UI test

[robstryker]

Fixes #249

Summary

• Add retry logic to handle StaleElementReferenceError in extension UI test
• Eliminates ~50% failure rate on Ubuntu CI builds

Problem

The extension installed UI test was flaky, failing approximately 50% of the time with:

StaleElementReferenceError: stale element reference: stale element not found in the current frame
  at async ExtensionsViewItem.getTitle()
  at async ExtensionsViewSection.findItem()

Root cause: Between finding the extension item and calling getTitle(), VS Code refreshes the extensions list DOM, making the element reference stale.

Solution

Added retry logic that:

• Wraps the find + getTitle operations in a try/catch retry loop
• Catches StaleElementReferenceError specifically
• Retries up to 3 times with 500ms delay between attempts
• Re-throws other errors immediately
• Re-throws on final retry if still failing

This handles the timing issue without making the test less strict - it still validates the extension is installed and has the correct name.

Test plan

• Run the UI tests multiple times to verify they no longer fail intermittently
• CI should now have consistently green builds on Ubuntu

🤖 Generated with Claude Code