docs: order navbar icons as GitHub then Slack

Moves the GitHub link out of githubUrl and into the explicit links
array so the navbar renders GitHub first, then Slack. Fumadocs
appends githubUrl after links, which previously put Slack first.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs-site/app/layout.config.tsx

@@ -1,4 +1,5 @@
 import type { BaseLayoutProps } from "fumadocs-ui/layouts/shared";
+import { GitHubIcon } from "@/components/github-icon";
 import { Logo } from "@/components/logo";
 import { SlackIcon } from "@/components/slack-icon";
 
@@ -7,8 +8,15 @@ export const baseOptions: BaseLayoutProps = {
     title: <Logo />,
     transparentMode: "top",
   },
-  githubUrl: "https://github.com/kaelio/ktx",
   links: [
+    {
+      type: "icon",
+      label: "GitHub",
+      icon: <GitHubIcon />,
+      text: "GitHub",
+      url: "https://github.com/kaelio/ktx",
+      external: true,
+    },
     {
       type: "icon",
       label: "Join the KTX Slack community",