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/@heroicons/react/24/outline/BookmarkSquareIcon.js

@@ -0,0 +1,26 @@
+const React = require("react");
+function BookmarkSquareIcon({
+  title,
+  titleId,
+  ...props
+}, svgRef) {
+  return /*#__PURE__*/React.createElement("svg", Object.assign({
+    xmlns: "http://www.w3.org/2000/svg",
+    fill: "none",
+    viewBox: "0 0 24 24",
+    strokeWidth: 1.5,
+    stroke: "currentColor",
+    "aria-hidden": "true",
+    "data-slot": "icon",
+    ref: svgRef,
+    "aria-labelledby": titleId
+  }, props), title ? /*#__PURE__*/React.createElement("title", {
+    id: titleId
+  }, title) : null, /*#__PURE__*/React.createElement("path", {
+    strokeLinecap: "round",
+    strokeLinejoin: "round",
+    d: "M16.5 3.75V16.5L12 14.25 7.5 16.5V3.75m9 0H18A2.25 2.25 0 0 1 20.25 6v12A2.25 2.25 0 0 1 18 20.25H6A2.25 2.25 0 0 1 3.75 18V6A2.25 2.25 0 0 1 6 3.75h1.5m9 0h-9"
+  }));
+}
+const ForwardRef = /*#__PURE__*/ React.forwardRef(BookmarkSquareIcon);
+module.exports = ForwardRef;