Add cross-link to NanoVNA-H documentation site

- Add social link in header pointing to nano-vna.l.zmesh.systems
- Add "Related Documentation" section on landing page with LinkCard

astro.config.mjs

@@ -14,6 +14,9 @@ export default defineConfig({
         alt: 'NanoVNA-F V3',
         src: './src/assets/logo.svg',
       },
+      social: [
+        { icon: 'external', label: 'NanoVNA-H Docs', href: 'https://nano-vna.l.zmesh.systems' },
+      ],
       customCss: ['./src/styles/custom.css', './src/styles/landing.css'],
       head: [
         {

src/content/docs/index.mdx

@@ -111,6 +111,12 @@ import frontView from '../../assets/screenshots/front-view.png';
   <LinkCard title="TDR Mode" description="Cable length and fault measurement" href="/how-to/measurement-tools/tdr-mode/" />
 </CardGrid>
 
+## Related Documentation
+
+Looking for the **NanoVNA-H**? The open-source NanoVNA-H covers 600 Hz to 2 GHz and has extensive firmware documentation for developers.
+
+<LinkCard title="NanoVNA-H Documentation" description="Open-source VNA — 600 Hz to 2 GHz, with firmware source and development guides" href="https://nano-vna.l.zmesh.systems/" />
+
 <div class="landing-footer">
 
 **NanoVNA-F V3** by SYSJOINT Information Technology Co., Ltd.