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/autoprefixer/lib/hacks/image-set.js

@@ -0,0 +1,18 @@
+let Value = require('../value')
+
+class ImageSet extends Value {
+  /**
+   * Use non-standard name for WebKit and Firefox
+   */
+  replace(string, prefix) {
+    let fixed = super.replace(string, prefix)
+    if (prefix === '-webkit-') {
+      fixed = fixed.replace(/("[^"]+"|'[^']+')(\s+\d+\w)/gi, 'url($1)$2')
+    }
+    return fixed
+  }
+}
+
+ImageSet.names = ['image-set']
+
+module.exports = ImageSet