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-inside-container/index.js

@@ -0,0 +1,23 @@
+import fs from 'node:fs';
+import isDocker from 'is-docker';
+
+let cachedResult;
+
+// Podman detection
+const hasContainerEnv = () => {
+	try {
+		fs.statSync('/run/.containerenv');
+		return true;
+	} catch {
+		return false;
+	}
+};
+
+export default function isInsideContainer() {
+	// TODO: Use `??=` when targeting Node.js 16.
+	if (cachedResult === undefined) {
+		cachedResult = hasContainerEnv() || isDocker();
+	}
+
+	return cachedResult;
+}