Redesign default error pages with cleaner, more user-friendly UI
- Replace single-line error text with centered, constrained-width layout
- Add SVG icon (circle with exclamation mark) with dark mode support
- Add "Try Again" button that reloads the page
- Add small developer hint pointing to logs/console
- Improve typography: 18px semibold title, 15px message
- Full dark mode support via CSS media query
- Consistent design across global-error, app-error, and pages/_error
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>