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/select-hose/test/fixtures.js

@@ -0,0 +1,14 @@
+var assert = require('assert');
+
+function expectData(stream, expected, callback) {
+  var actual = '';
+
+  stream.on('data', function(chunk) {
+    actual += chunk;
+  });
+  stream.on('end', function() {
+    assert.equal(actual, expected);
+    callback();
+  });
+}
+exports.expectData = expectData;