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/launch-editor/index.d.ts

@@ -0,0 +1,16 @@
+/**
+ * Launch an editor to open a file at a specific line and column.
+ *
+ * @param file File path with optional line and column numbers (e.g.
+ *   "/path/to/file.js:10:2").
+ * @param specifiedEditor Optional editor command or path to use. Will be
+ *   parsed using `shell-quote`.
+ * @param onErrorCallback Optional callback for handling errors.
+ */
+declare function launchEditor(
+  file: string,
+  specifiedEditor?: string | ((fileName: string, errorMessage: string | null) => void),
+  onErrorCallback?: (fileName: string, errorMessage: string | null) => void
+): void;
+
+export = launchEditor;