docs: add favicon.ico and explicit icon meta tags

Generate favicon.ico (16x16, 32x32, 48x48) from favicon.svg with
#48b18e fill color. Add explicit <link rel="icon"> tags for both
ICO and SVG formats in Starlight head config for broader browser
compatibility.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: lollipop-onl

apps/docs/astro.config.mjs

@@ -33,6 +33,14 @@ export default defineConfig({
         root: { label: "日本語", lang: "ja" },
       },
       head: [
+        {
+          tag: "link",
+          attrs: { rel: "icon", href: "/bee/favicon.ico", sizes: "48x48" },
+        },
+        {
+          tag: "link",
+          attrs: { rel: "icon", href: "/bee/favicon.svg", type: "image/svg+xml" },
+        },
         {
           tag: "meta",
           attrs: { property: "og:image", content: "https://nulab.github.io/bee/og-image.png" },