ci: add lighthouse performance and accessibility gate

[zainabwahab-eth]

Summary

Add Lighthouse CI checks for key frontend routes with enforced performance and accessibility budgets, SEO budget configuration, PR comment with scores, and committed baseline configuration.

• Add @lhci/cli and lighthouserc.cjs configuration
• Add GitHub Actions workflow (.github/workflows/lighthouse.yml) running on PRs to main
• Add preview script to frontend/package.json
• Fix pre-existing build-blocking syntax errors in App.tsx, ToastContext.tsx, Hero.tsx, SendXLMForm.tsx, TransactionTable.tsx, Toast.css, TaskSubmissionForm.tsx, and global.css to enable the production build needed for Lighthouse auditing

Closes #377

Routes tested

Route	Description
/	Landing page — primary entry point
/agents	Agent registry browser — public browsing page

Thresholds

Category	Threshold	Enforcement
Performance	≥ 80	Hard gate — CI fails
Accessibility	≥ 95	Hard gate — CI fails
SEO	≥ 80	Budget / warning
Best Practices	≥ 70	Informational

How it works

1. Build: npx vite build produces a production build in dist/
2. Serve: npx vite preview --host 0.0.0.0 --port 4173 serves the production build
3. Audit: Lighthouse CI runs 2 times per route against the served build
4. Assert: lighthouserc.cjs enforces performance ≥ 0.80 and accessibility ≥ 0.95
5. Report: Results are posted as a PR comment with a score table
6. Storage: Lighthouse reports are uploaded to temporary public storage

Files changed

File	Description
.github/workflows/lighthouse.yml	GitHub Actions workflow for Lighthouse CI
frontend/lighthouserc.cjs	Lighthouse CI configuration with budgets
frontend/package.json	Added preview script and @lhci/cli devDependency
frontend/package-lock.json	Updated lockfile
frontend/src/App.tsx	Fixed broken JSX structure (pre-existing)
frontend/src/context/ToastContext.tsx	Fixed duplicate declarations (pre-existing)
frontend/src/components/landing/Hero.tsx	Added motion import, fixed closing tags (pre-existing)
frontend/src/components/wallet/SendXLMForm.tsx	Fixed duplicate attributes and broken JSX (pre-existing)
frontend/src/components/wallet/TransactionTable.tsx	Removed trailing junk code (pre-existing)
frontend/src/components/common/Toast.css	Fixed duplicate CSS keyframes (pre-existing)
frontend/src/components/agents/TaskSubmissionForm.tsx	Fixed duplicate declarations, added missing imports (pre-existing)
frontend/src/styles/global.css	Fixed CSS @import order (pre-existing)

How to run locally

cd frontend
npm ci
npx vite build
npx lhci autorun

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