ci 👷: add GitHub Actions workflow for linting and testing

Set up comprehensive CI pipeline with three jobs:

- Lint: Runs ESLint and type checking
- Test: Executes test suite with Coveralls integration
- Build: Verifies package builds correctly

The workflow uses pnpm and caches dependencies for faster runs.

vitest.config.mjs

@@ -4,7 +4,7 @@ export default defineConfig({
   test: {
     coverage: {
       provider: 'v8',
-      reporter: ['html', 'json', 'text'],
+      reporter: ['html', 'json', 'lcov', 'text'],
       reportsDirectory: './coverage/vitest-reports',
       include: ['src/css-rules/**/*.ts', 'src/shared-utils/**/*.ts'],
       exclude: ['src/**/*.css.ts', 'src/**/*index.ts', 'src/**/*types.ts'],