docs: add Buy Me a Coffee button + FUNDING.yml

GitHub READMEs don't render JS, so use the static shields.io BMC badge
in your custom #5F7FFF color instead of the script tag. FUNDING.yml
adds the native Sponsor button to the repo sidebar.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/FUNDING.yml

@@ -0,0 +1 @@
+buy_me_a_coffee: hmbown

README.md

@@ -12,6 +12,8 @@ npm i -g deepseek-tui
 [![npm](https://img.shields.io/npm/v/deepseek-tui)](https://www.npmjs.com/package/deepseek-tui)
 [![crates.io](https://img.shields.io/crates/v/deepseek-tui-cli?label=crates.io)](https://crates.io/crates/deepseek-tui-cli)
 
+<a href="https://www.buymeacoffee.com/hmbown" target="_blank"><img src="https://img.shields.io/badge/Buy%20me%20a%20coffee-5F7FFF?style=for-the-badge&logo=buymeacoffee&logoColor=white" alt="Buy me a coffee" /></a>
+
 ![DeepSeek TUI screenshot](assets/screenshot.png)
 
 ---