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/onetime/index.js

@@ -0,0 +1,41 @@
+import mimicFunction from 'mimic-function';
+
+const calledFunctions = new WeakMap();
+
+const onetime = (function_, options = {}) => {
+	if (typeof function_ !== 'function') {
+		throw new TypeError('Expected a function');
+	}
+
+	let returnValue;
+	let callCount = 0;
+	const functionName = function_.displayName || function_.name || '<anonymous>';
+
+	const onetime = function (...arguments_) {
+		calledFunctions.set(onetime, ++callCount);
+
+		if (callCount === 1) {
+			returnValue = function_.apply(this, arguments_);
+			function_ = undefined;
+		} else if (options.throw === true) {
+			throw new Error(`Function \`${functionName}\` can only be called once`);
+		}
+
+		return returnValue;
+	};
+
+	mimicFunction(onetime, function_);
+	calledFunctions.set(onetime, callCount);
+
+	return onetime;
+};
+
+onetime.callCount = function_ => {
+	if (!calledFunctions.has(function_)) {
+		throw new Error(`The given function \`${function_.name}\` is not wrapped by the \`onetime\` package`);
+	}
+
+	return calledFunctions.get(function_);
+};
+
+export default onetime;