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/at-rule.js

@@ -0,0 +1,35 @@
+let Prefixer = require('./prefixer')
+
+class AtRule extends Prefixer {
+  /**
+   * Clone and add prefixes for at-rule
+   */
+  add(rule, prefix) {
+    let prefixed = prefix + rule.name
+
+    let already = rule.parent.some(
+      i => i.name === prefixed && i.params === rule.params
+    )
+    if (already) {
+      return undefined
+    }
+
+    let cloned = this.clone(rule, { name: prefixed })
+    return rule.parent.insertBefore(rule, cloned)
+  }
+
+  /**
+   * Clone node with prefixes
+   */
+  process(node) {
+    let parent = this.parentPrefix(node)
+
+    for (let prefix of this.prefixes) {
+      if (!parent || parent === prefix) {
+        this.add(node, prefix)
+      }
+    }
+  }
+}
+
+module.exports = AtRule