feat: Display a11y violations and conditional build report

Adds a section to the report viewer to display accessibility violations found by axe-core. This includes:
- A new A11y badge in the attempt header to indicate the presence of violations.
- A detailed breakdown of each violation, including its impact, description, a link to learn more, and the failing HTML elements.

This change also makes the build error section and badge only appear if there are build errors.

Author: tjshiu