chore: wide hero banner (21:9) — first image using aspect ratio support

1536x672 ultra-wide banner generated via img-forge ultra tier with
the new aspect_ratio parameter. Clean typographic design.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Kurt Overmier

README.md

@@ -2,7 +2,7 @@
 
 [![npm version](https://img.shields.io/npm/v/@stackbilt/cli?label=charter&color=5F7FFF&style=for-the-badge)](https://www.npmjs.com/package/@stackbilt/cli)
 
-![Charter Kit hero](./stackbilt-charter-3.png)
+![Charter Kit hero](./stackbilt-charter-4.png)
 
 ## The Problem