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/is-fullwidth-code-point/index.d.ts

@@ -0,0 +1,17 @@
+/**
+Check if the character represented by a given [Unicode code point](https://en.wikipedia.org/wiki/Code_point) is [fullwidth](https://en.wikipedia.org/wiki/Halfwidth_and_fullwidth_forms).
+
+@param codePoint - The [code point](https://en.wikipedia.org/wiki/Code_point) of a character.
+
+@example
+```
+import isFullwidthCodePoint from 'is-fullwidth-code-point';
+
+isFullwidthCodePoint('谢'.codePointAt(0));
+//=> true
+
+isFullwidthCodePoint('a'.codePointAt(0));
+//=> false
+```
+*/
+export default function isFullwidthCodePoint(codePoint: number): boolean;