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/minimalistic-assert/index.js

@@ -0,0 +1,11 @@
+module.exports = assert;
+
+function assert(val, msg) {
+  if (!val)
+    throw new Error(msg || 'Assertion failed');
+}
+
+assert.equal = function assertEqual(l, r, msg) {
+  if (l != r)
+    throw new Error(msg || ('Assertion failed: ' + l + ' != ' + r));
+};