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/lmdb/level.js

@@ -0,0 +1,27 @@
+export function levelup(store) {
+	return Object.assign(Object.create(store), {
+		get(key, options, callback) {
+			let result = store.get(key);
+			if (typeof options == 'function')
+				callback = options;
+			if (callback) {
+				if (result === undefined)
+					callback(new NotFoundError());
+				else
+					callback(null, result);
+			} else {
+				if (result === undefined)
+					return Promise.reject(new NotFoundError());
+				else
+					return Promise.resolve(result);
+			}
+		},
+	});
+}
+class NotFoundError extends Error {
+	constructor(message) {
+		super(message);
+		this.name = 'NotFoundError';
+		this.notFound = true;
+	}
+}