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.json

@@ -2,6 +2,7 @@
   "name": "@playwright/mcp",
   "version": "0.0.18",
   "description": "Playwright Tools for MCP",
+  "type": "module",
   "repository": {
     "type": "git",
     "url": "git+https://github.com/microsoft/playwright-mcp.git"