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/mkdirp/lib/use-native.js

@@ -0,0 +1,10 @@
+const fs = require('fs')
+
+const version = process.env.__TESTING_MKDIRP_NODE_VERSION__ || process.version
+const versArr = version.replace(/^v/, '').split('.')
+const hasNative = +versArr[0] > 10 || +versArr[0] === 10 && +versArr[1] >= 12
+
+const useNative = !hasNative ? () => false : opts => opts.mkdir === fs.mkdir
+const useNativeSync = !hasNative ? () => false : opts => opts.mkdirSync === fs.mkdirSync
+
+module.exports = {useNative, useNativeSync}