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/thingies/lib/createRace.d.ts

@@ -0,0 +1,27 @@
+/**
+ * Constructs a function that will only invoke the first function passed to it
+ * concurrently. Once the function has been executed, the racer will be reset
+ * and the next invocation will be allowed to execute.
+ *
+ * Example:
+ *
+ * ```ts
+ * import {createRace} from 'thingies/es2020/createRace';
+ *
+ * const race = createRace();
+ *
+ * race(() => {
+ *   race(() => {
+ *    console.log('This will not be executed');
+ *   });
+ *   console.log('This will be executed');
+ * });
+ *
+ * race(() => {
+ *  console.log('This will be executed');
+ * });
+ * ```
+ *
+ * @returns A "race" function that will only invoke the first function passed to it.
+ */
+export declare const createRace: () => <T>(fn: () => T) => T | undefined;