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

src/tab.ts

@@ -16,9 +16,9 @@
 
 import * as playwright from 'playwright';
 
-import { PageSnapshot } from './pageSnapshot';
+import { PageSnapshot } from './pageSnapshot.js';
 
-import type { Context } from './context';
+import type { Context } from './context.js';
 
 export class Tab {
   readonly context: Context;