See parent task t-3594 for full context.

What#

Final polish phase after all other phases are complete:

1. Export: Add JSON/MD export for benchmark reports.
2. Trend charts: Line chart showing model score over time across multiple runs.
3. Notifications: Toast or in-app notification when benchmark completes.
4. Shareable links: Copy-to-clipboard permalink for specific results.
5. Tests: Full test coverage for all new lib modules, components, API routes.
6. Edge case coverage: Empty state, errors, long prompts, concurrent runs.
7. Responsive: Works on mobile (min 320px).

Tags#

[benchmarks, polish, tests, export]