feat: add cross-browser extension with AI reading assistant

- Create Pi Reader browser extension for Chrome/Firefox
- Chrome uses Side Panel API, Firefox uses Sidebar Action API
- Supports both browsers with separate manifests and unified codebase
- Built with mini-lit components and Tailwind CSS v4
- Features model selection dialog with Ollama support
- Hot reload development server watches both browser builds
- Add useDefineForClassFields: false to fix LitElement reactivity

packages/browser-extension/tsconfig.json

@@ -0,0 +1,6 @@
+{
+  "extends": "./tsconfig.build.json",
+  "compilerOptions": {
+    "noEmit": true
+  }
+}