chore: migrate to ESM (#303)

- [Why do I need `.js`
extension?](https://stackoverflow.com/a/77150985/6512681)
- [Why setting `rootDir` in the
`tsconfig.json`?](https://stackoverflow.com/a/58941798/6512681)
- [How to ensure that we add the `.js` extension via
ESLint](https://github.com/import-js/eslint-plugin-import/blob/main/docs/rules/extensions.md#importextensions)

Fixes https://github.com/microsoft/playwright-mcp/issues/302

package-lock.json

@@ -16,7 +16,7 @@
         "zod-to-json-schema": "^3.24.4"
       },
       "bin": {
-        "mcp-server-playwright": "cli.js"
+        "mcp-server-playwright": "cli.mjs"
       },
       "devDependencies": {
         "@eslint/eslintrc": "^3.2.0",