docs(design): remove SVG, use PNG logo only

SVG icon is no longer in use. public/logo.png (1024x1024 RGBA) is
the single logo asset. DESIGN.md updated accordingly: SVG snippet
removed, wordmark pattern and <head> references updated to PNG.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

node_modules/postcss-js/README.md

@@ -0,0 +1,22 @@
+# PostCSS JS
+
+<img align="right" width="135" height="95"
+     title="Philosopher’s stone, logo of PostCSS"
+     src="https://postcss.org/logo-leftp.svg">
+
+[PostCSS] for CSS-in-JS and styles in JS objects.
+
+For example, to use [Stylelint] or [RTLCSS] plugins in your workflow.
+
+<a href="https://evilmartians.com/?utm_source=postcss-js">
+  <img src="https://evilmartians.com/badges/sponsored-by-evil-martians.svg"
+       alt="Sponsored by Evil Martians" width="236" height="54">
+</a>
+
+[Stylelint]: https://github.com/stylelint/stylelint
+[PostCSS]:   https://github.com/postcss/postcss
+[RTLCSS]:    https://github.com/MohammadYounes/rtlcss
+
+
+## Docs
+Read full docs **[here](https://github.com/postcss/postcss-js#readme)**.