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/src/app.css

@@ -0,0 +1,14 @@
+/* Import Claude theme from mini-lit */
+@import "@mariozechner/mini-lit/styles/themes/default.css";
+
+/* Tell Tailwind to scan mini-lit components */
+@source "../../../node_modules/@mariozechner/mini-lit/dist";
+
+/* Import Tailwind */
+/* biome-ignore lint/correctness/noInvalidPositionAtImportRule: fuck you */
+@import "tailwindcss";
+
+body {
+	font-size: 16px;
+	-webkit-font-smoothing: antialiased;
+}