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/autoprefixer/lib/hacks/image-set.js

@@ -0,0 +1,18 @@
+let Value = require('../value')
+
+class ImageSet extends Value {
+  /**
+   * Use non-standard name for WebKit and Firefox
+   */
+  replace(string, prefix) {
+    let fixed = super.replace(string, prefix)
+    if (prefix === '-webkit-') {
+      fixed = fixed.replace(/("[^"]+"|'[^']+')(\s+\d+\w)/gi, 'url($1)$2')
+    }
+    return fixed
+  }
+}
+
+ImageSet.names = ['image-set']
+
+module.exports = ImageSet