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/istanbul-lib-coverage/lib/data-properties.js

@@ -0,0 +1,12 @@
+'use strict';
+
+module.exports = function dataProperties(klass, properties) {
+    properties.forEach(p => {
+        Object.defineProperty(klass.prototype, p, {
+            enumerable: true,
+            get() {
+                return this.data[p];
+            }
+        });
+    });
+};