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-network-error/index.js

@@ -0,0 +1,43 @@
+const objectToString = Object.prototype.toString;
+
+const isError = value => objectToString.call(value) === '[object Error]';
+
+const errorMessages = new Set([
+	'network error', // Chrome
+	'Failed to fetch', // Chrome
+	'NetworkError when attempting to fetch resource.', // Firefox
+	'The Internet connection appears to be offline.', // Safari 16
+	'Network request failed', // `cross-fetch`
+	'fetch failed', // Undici (Node.js)
+	'terminated', // Undici (Node.js)
+	' A network error occurred.', // Bun (WebKit)
+	'Network connection lost', // Cloudflare Workers (fetch)
+]);
+
+export default function isNetworkError(error) {
+	const isValid = error
+		&& isError(error)
+		&& error.name === 'TypeError'
+		&& typeof error.message === 'string';
+
+	if (!isValid) {
+		return false;
+	}
+
+	const {message, stack} = error;
+
+	// Safari 17+ has generic message but no stack for network errors
+	if (message === 'Load failed') {
+		return stack === undefined
+			// Sentry adds its own stack trace to the fetch error, so also check for that
+			|| '__sentry_captured__' in error;
+	}
+
+	// Deno network errors start with specific text
+	if (message.startsWith('error sending request for url')) {
+		return true;
+	}
+
+	// Standard network error messages
+	return errorMessages.has(message);
+}