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/@babel/runtime/helpers/using.js

@@ -0,0 +1,12 @@
+function _using(o, n, e) {
+  if (null == n) return n;
+  if (Object(n) !== n) throw new TypeError("using declarations can only be used with objects, functions, null, or undefined.");
+  if (e) var r = n[Symbol.asyncDispose || Symbol["for"]("Symbol.asyncDispose")];
+  if (null == r && (r = n[Symbol.dispose || Symbol["for"]("Symbol.dispose")]), "function" != typeof r) throw new TypeError("Property [Symbol.dispose] is not a function.");
+  return o.push({
+    v: n,
+    d: r,
+    a: e
+  }), n;
+}
+module.exports = _using, module.exports.__esModule = true, module.exports["default"] = module.exports;