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/TimedState.d.ts

@@ -0,0 +1,26 @@
+/**
+ * TimedState works similar to TimedQueue, but instead of saving
+ * a list of all items pushed, it reduces the state on each push.
+ */
+export declare class TimedState<S, I> {
+    protected readonly initState: () => S;
+    protected readonly reducer: (state: S, item: I) => S;
+    /**
+     * State will be flushed when it reaches this number of items.
+     */
+    itemLimit: number;
+    /**
+     * State will be flushed after this many milliseconds.
+     */
+    timeLimit: number;
+    /**
+     * Method that will be called when state is flushed.
+     */
+    onFlush: (state: S) => void;
+    constructor(initState: () => S, reducer: (state: S, item: I) => S);
+    protected length: number;
+    protected state: S;
+    private timer;
+    push(item: I): void;
+    flush(): S;
+}