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/display-grid.js

@@ -0,0 +1,21 @@
+let Value = require('../value')
+
+class DisplayGrid extends Value {
+  constructor(name, prefixes) {
+    super(name, prefixes)
+    if (name === 'display-grid') {
+      this.name = 'grid'
+    }
+  }
+
+  /**
+   * Faster check for flex value
+   */
+  check(decl) {
+    return decl.prop === 'display' && decl.value === this.name
+  }
+}
+
+DisplayGrid.names = ['display-grid', 'inline-grid']
+
+module.exports = DisplayGrid