docs: add banner image

Author: Kikobeats

design/banner.sketch

@@ -9,7 +9,7 @@
   <meta name="description" content="Run JavaScript from AI agents, plugins, and workflows in a separate Node.js process with strict permissions, dependency allowlists, and resource limits." />
   <meta name="keywords" content="isolated-function, Node.js sandbox, untrusted JavaScript, v8 sandbox, secure code execution, package dependency allowlist" />
   <meta name="robots" content="index, follow, max-image-preview:large" />
-  <meta name="image" content="https://kikobeats.github.io/isolated-function/static/logo.png" />
+  <meta name="image" content="https://kikobeats.github.io/isolated-function/static/banner.png" />
   <meta name="theme-color" content="#f2f0ea" />
   <link rel="canonical" href="https://kikobeats.github.io/isolated-function/" />
   <link rel="alternate" type="text/markdown" href="https://kikobeats.github.io/isolated-function/README.md" title="isolated-function documentation markdown" />
@@ -19,8 +19,10 @@
 
   <meta property="og:title" content="isolated-function: Node.js Sandbox for Untrusted Code" />
   <meta property="og:description" content="Run JavaScript from AI agents, plugins, and workflows in a separate Node.js process with strict permissions, dependency allowlists, and resource limits." />
-  <meta property="og:image" content="https://kikobeats.github.io/isolated-function/static/logo.png" />
-  <meta property="og:image:alt" content="isolated-function package logo" />
+  <meta property="og:image" content="https://kikobeats.github.io/isolated-function/static/banner.png" />
+  <meta property="og:image:width" content="2400" />
+  <meta property="og:image:height" content="1256" />
+  <meta property="og:image:alt" content="isolated-function banner with cube logo and sandbox tagline" />
   <meta property="og:url" content="https://kikobeats.github.io/isolated-function/" />
   <meta property="og:site_name" content="isolated-function" />
   <meta property="og:type" content="website" />
@@ -31,8 +33,8 @@
   <meta name="twitter:creator" content="@Kikobeats" />
   <meta name="twitter:title" content="isolated-function: Node.js Sandbox for Untrusted Code" />
   <meta name="twitter:description" content="Run JavaScript from AI agents, plugins, and workflows in a separate Node.js process with strict permissions, dependency allowlists, and resource limits." />
-  <meta name="twitter:image" content="https://kikobeats.github.io/isolated-function/static/logo.png" />
-  <meta name="twitter:image:alt" content="isolated-function package logo" />
+  <meta name="twitter:image" content="https://kikobeats.github.io/isolated-function/static/banner.png" />
+  <meta name="twitter:image:alt" content="isolated-function banner with cube logo and sandbox tagline" />
 
   <script type="application/ld+json">
   {