feat: integrate lighthouse-ci

[Jetshree]

What does this PR change?

• Integrates Lighthouse CI into the GitHub Actions workflow.
• Adds automated performance, accessibility, best practices, and SEO audits for every PR and push to main.
• Configures score assertions to help prevent regressions.
• Uploads Lighthouse reports as CI artifacts for debugging and visibility.

Does this PR relate to any other PRs?

• No

How will this PR impact users?

• This change does not directly impact end users.
• It improves overall UI quality by automatically detecting performance and accessibility regressions before merging.
• Helps maintain a consistent and reliable user experience over time.

Does this PR address any GitHub or Zendesk issues?

• Closes Introduce Lighthouse CI #219

How was this PR tested?

Does this PR require changes to documentation?

• No

Have you labeled this PR and its corresponding Issue as "next release" if it should be part of the next OpenCost release? If not, why not?

• Yes

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