Add Lighthouse CI configuration

[ChadOhman]

📝 Pull Request

Description

• add Lighthouse CI config covering key pages with mobile-focused thresholds
• create GitHub Actions workflow to run LHCI and publish artifacts
• document automated quality checks and ignore LHCI outputs

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist

• My code follows the project's coding standards
• I have tested my changes locally
• I have updated documentation (README/QUICKSTART) if necessary
• I have added tests or ensured existing tests pass

Screenshots (if applicable)

N/A

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Codex Task