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/unicode-match-property-value-ecmascript/index.js

@@ -0,0 +1,19 @@
+'use strict';
+
+const propertyToValueAliases = require('./data/mappings.js');
+
+const matchPropertyValue = function(property, value) {
+	const aliasToValue = propertyToValueAliases.get(property);
+	if (!aliasToValue) {
+		throw new Error(`Unknown property \`${ property }\`.`);
+	}
+	const canonicalValue = aliasToValue.get(value);
+	if (canonicalValue) {
+		return canonicalValue;
+	}
+	throw new Error(
+		`Unknown value \`${ value }\` for property \`${ property }\`.`
+	);
+};
+
+module.exports = matchPropertyValue;