Implement GitHub Actions CI pipeline for Next.js build

[Code-Paragon]

Problem

Incoming pull requests are not automatically checked for build errors or linting violations, pushing the manual testing burden onto the core maintainers.

Expected behavior

A GitHub Actions workflow is triggered on every PR to main that runs npm ci, npm run lint, and npm run build to verify the application compiles successfully.

Files to update

• .github/workflows/frontend-ci.yml (create)

Project relevance

Automates code quality gates, ensuring that broken styles, missing imports, or TypeScript regressions never reach the production branch.

Acceptance criteria

• Feature works as described
• Tests are added or updated where needed
• Documentation is updated where needed
• Workflow uses Node.js v18 and caches node_modules for speed
• No TypeScript, lint, test, or build errors