Initial commit: notification-elements-demo app

Interactive Angular 19 demo for @sda/notification-elements-ui with
6 sections: Bell & Feed, Notification Center, Inbox, Comments &
Threads, Mention Input, and Full-Featured layout. Includes mock
data, dark mode toggle, and real-time event log.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

node_modules/default-browser/index.d.ts

@@ -0,0 +1,29 @@
+export type Browser = {
+	/**
+	Human-readadable name of the browser.
+	*/
+	name: string;
+
+	/**
+	The unique identifier for the browser on the current platform:
+	- On macOS, it's the app's bundle identifier.
+	- On Linux, it's the desktop file identifier (from `xdg-mime`).
+	- On Windows, it's an invented identifier, because apps on Windows does not have identifiers.
+	*/
+	id: string;
+};
+
+/**
+Get the default browser for the current platform.
+
+@returns A promise for the browser.
+
+@example
+```
+import defaultBrowser from 'default-browser';
+
+console.log(await defaultBrowser());
+//=> {name: 'Safari', id: 'com.apple.Safari'}
+```
+*/
+export default function defaultBrowser(): Promise<Browser>;