feat(web): add Plausible analytics snippet to the shared layout footer

Self-hosted Plausible instance at a.w5isp.com. No cookies, no personal
data; drops one small JS file per page view.

lib/microwaveprop_web/components/layouts.ex

@@ -106,6 +106,13 @@ defmodule MicrowavepropWeb.Layouts do
       </div>
     </footer>
 
+    <!-- Privacy-friendly analytics by Plausible -->
+    <script async src="https://a.w5isp.com/js/pa-3eKACFxtbw6MHrTDA28wG.js"></script>
+    <script>
+      window.plausible=window.plausible||function(){(plausible.q=plausible.q||[]).push(arguments)},plausible.init=plausible.init||function(i){plausible.o=i||{}};
+      plausible.init()
+    </script>
+
     <.flash_group flash={@flash} />
     """
   end