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/msgpackr-extract/bin/download-prebuilds.js

@@ -0,0 +1,13 @@
+#!/usr/bin/env node
+
+const { dirname } = require('path');
+const { fileURLToPath } = require('url');
+const { exec } = require('child_process');
+
+process.chdir(dirname(__dirname));
+exec('prebuildify-ci download', (error, stdout, stderr) => {
+	console.error(stderr);
+	console.log(stdout);
+	if (error?.code)
+		process.exit(error.code);
+});