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/lines-and-columns/build/index.d.ts

@@ -0,0 +1,13 @@
+export declare type SourceLocation = {
+    line: number;
+    column: number;
+};
+export declare class LinesAndColumns {
+    private string;
+    private offsets;
+    constructor(string: string);
+    locationForIndex(index: number): SourceLocation | null;
+    indexForLocation(location: SourceLocation): number | null;
+    private lengthOfLine;
+}
+export default LinesAndColumns;