Add GitHub Actions CI

[chiragborse1]

Summary

• Add a CI workflow for pull requests and pushes to main.
• Run frozen pnpm install, typecheck, tests, and production build.
• Use current major GitHub Actions for checkout, Node.js setup, and pnpm setup.

Validation

• pnpm install --frozen-lockfile
• pnpm typecheck
• pnpm test
• pnpm build

[chiragborse1]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved the merge conflicts and pushed the fix in commit 7dea6b6.