refactor: reorganize README.md structure and update image paths

Moved documentation assets from docs/ to assets/ directory and updated README.md to use new paths. Restructured the header format for better visual presentation with a code block style title and updated badge references.

Author: involvex

README.md

@@ -1,6 +1,9 @@
-# @involvex/super-agent-cli
+```
+              @involvex/super-agent-cli
+```
+
+![Super Agent CLI Banner](assets/images/banner.png)
 
-![Super Agent CLI Banner](docs/banner.png)
 [![Security Scan](https://github.com/involvex/super-agent-cli/actions/workflows/security.yml/badge.svg)](https://github.com/involvex/super-agent-cli/actions/workflows/security.yml)
 ![Badge](https://img.shields.io/npm/v/@involvex/super-agent-cli?label=build&message=passing&color=brightgreen&style=social&logo=npm)