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/exponential-backoff/dist/delay/delay.base.d.ts

@@ -0,0 +1,12 @@
+import { IDelay } from "./delay.interface";
+import { IBackOffOptions } from "../options";
+export declare abstract class Delay implements IDelay {
+    private options;
+    protected attempt: number;
+    constructor(options: IBackOffOptions);
+    apply(): Promise<unknown>;
+    setAttemptNumber(attempt: number): void;
+    private readonly jitteredDelay;
+    private readonly delay;
+    protected readonly numOfDelayedAttempts: number;
+}