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/lib/document.js

@@ -0,0 +1,33 @@
+'use strict'
+
+let Container = require('./container')
+
+let LazyResult, Processor
+
+class Document extends Container {
+  constructor(defaults) {
+    // type needs to be passed to super, otherwise child roots won't be normalized correctly
+    super({ type: 'document', ...defaults })
+
+    if (!this.nodes) {
+      this.nodes = []
+    }
+  }
+
+  toResult(opts = {}) {
+    let lazy = new LazyResult(new Processor(), this, opts)
+
+    return lazy.stringify()
+  }
+}
+
+Document.registerLazyResult = dependant => {
+  LazyResult = dependant
+}
+
+Document.registerProcessor = dependant => {
+  Processor = dependant
+}
+
+module.exports = Document
+Document.default = Document