Site audit fixes: metadata, download URLs, nav dropdown, CTAs, related resources

- Add metadata and h1 to homepage
- Replace all placeholder download URLs with real links
- Convert Platform nav item to dropdown with product sub-links
- Add hero CTA buttons to rover page
- Add bottom CTA section to platform page
- Add RelatedResources to junior and python pages
- Add metadata description to contact and download pages
- Update "Visit Store" to "Build Your Kit" for consistency
- Add Airtable TODO comment in contact form handler
- Update Micromelon-Py card image to VS Code screenshot

src/app/rover/page.tsx

@@ -117,6 +117,14 @@ export default function RoverPage() {
                 Long battery life, tough, and packed with sensors to make a
                 great classroom tool. Connect and run code in seconds.
               </p>
+              <div className="mt-8 flex flex-col gap-3 sm:flex-row">
+                <Button href="/store" variant="primary">
+                  Build Your Kit
+                </Button>
+                <Button href="/download" variant="outline">
+                  Download Code Editor
+                </Button>
+              </div>
             </div>
             <div>
               <Image
@@ -193,7 +201,7 @@ export default function RoverPage() {
                 Expansion &amp; 3D Printing
               </Button>
               <Button href="/store" variant="outline">
-                Visit Store
+                Build Your Kit
               </Button>
             </div>
           </div>