Add Umami analytics in production

Script injected via hugo.IsProduction guard so it's absent during
hugo server dev mode. Src and website-id stored in hugo.toml params.

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

layouts/partials/head.html

@@ -27,4 +27,7 @@
 <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
 <link href="https://fonts.googleapis.com/css2?family=Italiana&family=Cormorant+Garamond:ital,wght@0,300;0,400;0,500;0,600;1,300;1,400;1,500&family=Outfit:wght@300;400;500;600&family=JetBrains+Mono:wght@400;500&display=swap" rel="stylesheet" />
 <link rel="stylesheet" href="/css/main.css" />
+{{- if hugo.IsProduction }}
+<script defer src="{{ .Site.Params.umamiSrc }}" data-website-id="{{ .Site.Params.umamiId }}"></script>
+{{- end }}
 {{ with .OutputFormats.Get "RSS" }}<link rel="alternate" type="{{ .MediaType.Type }}" title="{{ $.Site.Title }}" href="{{ .Permalink }}" />{{ end }}