feat(website): Umami analytics (conversion + CTA events)

Add the Umami tracker (cookieless, no consent banner) in the document head,
limited to the production hostnames via data-domains so dev traffic doesn't
pollute the stats. Pageviews are auto-tracked per page and locale.

Custom events on the key funnel:
- demo-request (demo form submit, with teamSize)
- partner-application (partner form submit, with type)
- book-demo (every "Book a demo" CTA click) via data-umami-event
- login (clicks through to the app)

Also fix the mobile nav menu links, which weren't localized (would drop
Danish visitors back to English).

apps/website/pages/contact.vue

@@ -57,7 +57,7 @@ useHead({ title: () => `${copy.value.pages.contact.label} · dezky` })
         <div>
           <h2 :style="h2">{{ c.demoHeading }}</h2>
           <p :style="{ fontFamily: '\'Inter\', sans-serif', fontSize: '18px', lineHeight: 1.6, color: t.fgMuted, margin: '18px 0 28px', textWrap: 'pretty' }">{{ c.demoBody }}</p>
-          <LandingBtn variant="primary" size="lg" @click="navigateTo(localePath('/demo'))">{{ copy.pages.ctaDemo }} →</LandingBtn>
+          <LandingBtn variant="primary" size="lg" data-umami-event="book-demo" @click="navigateTo(localePath('/demo'))">{{ copy.pages.ctaDemo }} →</LandingBtn>
         </div>
       </div>
     </div>