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/is-docker/index.js

@@ -0,0 +1,29 @@
+import fs from 'node:fs';
+
+let isDockerCached;
+
+function hasDockerEnv() {
+	try {
+		fs.statSync('/.dockerenv');
+		return true;
+	} catch {
+		return false;
+	}
+}
+
+function hasDockerCGroup() {
+	try {
+		return fs.readFileSync('/proc/self/cgroup', 'utf8').includes('docker');
+	} catch {
+		return false;
+	}
+}
+
+export default function isDocker() {
+	// TODO: Use `??=` when targeting Node.js 16.
+	if (isDockerCached === undefined) {
+		isDockerCached = hasDockerEnv() || hasDockerCGroup();
+	}
+
+	return isDockerCached;
+}