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/README.md

@@ -0,0 +1,33 @@
+# lines-and-columns
+
+Maps lines and columns to character offsets and back. This is useful for parsers
+and other text processors that deal in character ranges but process text with
+meaningful lines and columns.
+
+## Install
+
+```
+$ npm install [--save] lines-and-columns
+```
+
+## Usage
+
+```js
+import { LinesAndColumns } from 'lines-and-columns'
+
+const lines = new LinesAndColumns(
+  `table {
+  border: 0
+}`
+)
+
+lines.locationForIndex(9)
+// { line: 1, column: 1 }
+
+lines.indexForLocation({ line: 1, column: 2 })
+// 10
+```
+
+## License
+
+MIT