Add CI to run lint and type-check on PRs

[sugan0tech]

Summary
Add CI (GitHub Actions) to run lint and type-check on pull requests and main.

Context
Currently there is no automated check to block merges that break linting or typing.

Tasks

• Add .github/workflows/ci.yml that runs on push to main and pull_request.
• Setup Node (latest LTS) and cache npm; install with npm ci.
• Run npm run lint and tsc -b. Optionally add vite build.
• Document the workflow briefly in README and optionally add a status badge.

Acceptance Criteria

• CI runs successfully on new PRs and main pushes.
• PRs fail when lint/type-check fails.
• Minimal runtime (fast feedback) with dependency caching.