[CI/CD] Add Lighthouse SEO/Accessibility Auditing & Fix Jekyll Caching #1909

Problem

Website SEO, accessibility, and loading performance regressions aren't currently checked in PRs.
The build-and-deploy.yml workflow specifies a checkout action which does not exist or has an invalid version.
Additionally, build-and-deploy.yml runs bundle install manually on every run without utilizing the setup-ruby bundler-cache feature, significantly slowing down deployment and PR feedback.

Proposed Changes

• Implement lighthouse-ci-action in .github/workflows/lighthouse.yml.
• Validate URLs representing key page layouts via .lighthouserc.json.
• Repair formatting of checkout and enable bundler-cache in build-and-deploy.yml.

This drastically cuts CI execution times and prevents performance regressions.