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/Cache.d.ts

@@ -0,0 +1,26 @@
+export interface CacheEntry<T> {
+    t: number;
+    value: T;
+}
+export declare class Cache<T> {
+    method: (key: string) => Promise<T>;
+    ttl: number;
+    evictionTime: number;
+    gcPeriod: number;
+    maxEntries: number;
+    private entries;
+    map: Map<string, CacheEntry<T>>;
+    private timer;
+    constructor(method?: (key: string) => Promise<T>);
+    put(key: string, value: T): void;
+    getFromSource(key: string): Promise<T>;
+    get(key: string): Promise<T>;
+    getSync(key: string): T | null;
+    exists(key: string): boolean;
+    scheduleGC(): void;
+    startGC(): void;
+    runGC: () => void;
+    stopGC: () => void;
+    retire(key: string, newTime?: number): boolean;
+    remove(key: string): boolean;
+}