feat(docs): add gem favicon to VitePress site

apps/docs/.vitepress/config.mts

@@ -7,7 +7,10 @@ export default defineConfig({
   srcDir: ".",
   outDir: "./.vitepress/dist",
 
-  head: [["meta", { name: "theme-color", content: "#3b82f6" }]],
+  head: [
+    ["meta", { name: "theme-color", content: "#3b82f6" }],
+    ["link", { rel: "icon", type: "image/svg+xml", href: "/Stirling-Image/favicon.svg" }],
+  ],
 
   themeConfig: {
     nav: [

apps/docs/public/favicon.svg

@@ -0,0 +1,7 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 140 140" fill="none">
+  <polygon points="70,16 100,48 70,60 40,48" fill="#3b82f6"/>
+  <polygon points="40,48 70,60 70,124 22,60" fill="#3b82f6" opacity="0.7"/>
+  <polygon points="100,48 70,60 70,124 118,60" fill="#3b82f6" opacity="0.5"/>
+  <polygon points="70,16 40,48 22,60" fill="#3b82f6" opacity="0.85"/>
+  <polygon points="70,16 100,48 118,60" fill="#3b82f6" opacity="0.65"/>
+</svg>