feat(infra): Add Lighthouse CI for client performance budgets

[rahimatonize]

Summary
This PR implements automated performance monitoring using Lighthouse CI to enforce Core Web Vitals thresholds and prevent performance regressions in the client application.

Changes Made

1. Lighthouse CI Configuration (
   lighthouserc.json
   )
   Created configuration file with performance budgets
   Core Web Vitals Assertions:
   ✅ LCP (Largest Contentful Paint): < 2.5s (error threshold)
   ✅ CLS (Cumulative Layout Shift): < 0.1 (error threshold)
   ✅ FCP (First Contentful Paint): < 2.0s (warning threshold)
   Additional metrics monitored: Speed Index, Interactive, TBT
   Performance score minimum: 90%
   Runs 3 audits per PR and takes median values
   Results uploaded to temporary public storage (7-day retention)
2. GitHub Actions Integration (
   ci.yml
   )
   Added new lighthouse job that:
   Depends on successful client build job
   Downloads pre-built client artifacts (no rebuild needed)
   Starts preview server automatically
   Runs Lighthouse audits
   Comments on PRs with performance metrics and report link
   Fails CI if LCP > 2.5s or CLS > 0.1
   Updated ci-summary job to include lighthouse results
3. Dependencies (
   package.json
   )
   Added @lhci/cli v0.14.0 as dev dependency
   Added npm scripts:
   pnpm run lighthouse - Run Lighthouse on existing build
   pnpm run lighthouse:local - Build and run Lighthouse locally
4. Documentation (
   LIGHTHOUSE_CI.md
   )
   Comprehensive guide on Lighthouse CI setup
   Performance optimization tips for each Core Web Vital
   Troubleshooting section
   Local testing instructions
5. Gitignore (
   .gitignore
   )
   Added .lighthouseci/ to exclude local Lighthouse results
   Acceptance Criteria Met
   ✅ A PR that regresses LCP beyond 2.5s causes the CI Lighthouse job to fail
   ✅ A PR that regresses CLS beyond 0.1 causes the CI Lighthouse job to fail
   ✅ The LHCI report is accessible via a link in the PR comment
   ✅ Results are uploaded to public storage for 30 days
   ✅ CI workflow integrates seamlessly with existing jobs

Testing
To test this locally:

cd client
pnpm install
pnpm run lighthouse:local
The Lighthouse report will be generated and a public link will be provided.

What Happens Now
When this PR is merged:

All future PRs will automatically run Lighthouse CI
Performance regressions will be caught before merge
Each PR will get a comment with performance scores and report link
The CI will fail if critical thresholds are exceeded
Additional Notes
The lighthouse job runs after the client build completes to save CI time
Desktop preset is used for consistent results
Results are stored for 30 days in GitHub artifacts
No secrets required for basic functionality (LHCI_GITHUB_APP_TOKEN is optional)
Closes #923

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