feat: variantes svg des icônes (square, foreground, monochrome)

docs/branding/icon-monochrome.svg

@@ -0,0 +1,9 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="512" height="512" viewBox="0 0 108 108" role="img" aria-labelledby="title">
+  <title id="title">Livrets — couche monochrome adaptive</title>
+  <g transform="translate(54,54) scale(0.5073) translate(-64,-64)">
+    <rect x="18" y="18" width="42" height="42" rx="12" fill="#FFFFFF"/>
+    <rect x="68" y="18" width="42" height="42" rx="12" fill="#FFFFFF"/>
+    <rect x="18" y="68" width="42" height="42" rx="12" fill="#FFFFFF"/>
+    <rect x="68" y="68" width="42" height="42" rx="12" fill="#FFFFFF"/>
+  </g>
+</svg>