ci: add bundle analysis to frontend CI pipeline

[YaronZaki]

Summary

The frontend CI pipeline built Next.js successfully but never ran bundle analysis, so bundle size regressions (e.g. from accidentally importing a large library) went completely undetected. The @next/bundle-analyzer package was already installed in analytics/ and configured in analytics/next.config.ts via ANALYZE=true — it just was not wired into CI.

This PR enables bundle analysis on every CI run, uploads the report as an artifact, and adds a chunk size threshold check that fails the build if any JS chunk exceeds 500 KB.

Changes

• Set ANALYZE: true on the Next.js build step so @next/bundle-analyzer generates the report
• Added a bundle size threshold check step that scans all .next/static/chunks/*.js files and fails if any exceeds 500,000 bytes
• Added Upload bundle analysis report artifact step (retains .next/analyze/ and .next/static/ for 30 days, runs on success and failure)
• Kept the existing build artifact upload unchanged

Testing

• CI workflow YAML validated (no syntax errors)
• Bundle analysis report generated locally with ANALYZE=true npm run build
• Size threshold script tested against .next/static/chunks/ output

Closes #39