Add tests for redesigned default error page UI
Tests verify:
- SVG icon is rendered
- Error title and message are displayed
- "Try Again" button is present and functional
- Developer hint shows correct log location (browser console vs server logs)
- Error ID is displayed for server-side errors
- Proper red styling on title and button
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
