feat: Domain-based routing — marketing site at bare domain, panel at subdomain

corrosionmgmt.com now serves LandingView as the default page with marketing
routes at root level. panel.corrosionmgmt.com continues serving the admin
panel unchanged. /site/* backward compat via redirects on marketing domain.

- nginx: Add bare domain server block (only proxies /api/early-access/)
- router: Detect hostname at module load, generate domain-specific routes
- MarketingLayout: Named routes for nav, external <a> tags for auth links
- LandingView: CTAs point to panel domain via VITE_PANEL_URL

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

frontend/src/views/marketing/LandingView.vue

@@ -1,6 +1,7 @@
 <script setup lang="ts">
-import { RouterLink } from 'vue-router'
 import { Shield, Zap, RefreshCw, Terminal, Users, Wifi, Server, ChevronRight } from 'lucide-vue-next'
+
+const panelUrl = import.meta.env.VITE_PANEL_URL || ''
 </script>
 
 <template>
@@ -16,9 +17,9 @@ import { Shield, Zap, RefreshCw, Terminal, Users, Wifi, Server, ChevronRight } f
           Deploy once. Automate everything. Never SSH again.
         </p>
         <div class="flex items-center justify-center gap-4">
-          <RouterLink to="/register" class="px-8 py-3.5 bg-oxide-600 hover:bg-oxide-700 text-white font-semibold rounded-lg transition-colors text-lg">
+          <a :href="panelUrl + '/register'" class="px-8 py-3.5 bg-oxide-600 hover:bg-oxide-700 text-white font-semibold rounded-lg transition-colors text-lg">
             Buy License
-          </RouterLink>
+          </a>
           <a href="#demo" class="px-8 py-3.5 bg-neutral-800 hover:bg-neutral-700 text-neutral-200 font-semibold rounded-lg border border-neutral-700 transition-colors text-lg">
             View Live Demo
           </a>
@@ -278,9 +279,9 @@ import { Shield, Zap, RefreshCw, Terminal, Users, Wifi, Server, ChevronRight } f
       <div class="max-w-3xl mx-auto px-6 text-center">
         <p class="text-2xl text-neutral-400 mb-2">Stop babysitting your server.</p>
         <p class="text-3xl font-bold text-neutral-100 mb-10">Start orchestrating it.</p>
-        <RouterLink to="/register" class="inline-block px-10 py-4 bg-oxide-600 hover:bg-oxide-700 text-white font-semibold rounded-lg transition-colors text-lg">
+        <a :href="panelUrl + '/register'" class="inline-block px-10 py-4 bg-oxide-600 hover:bg-oxide-700 text-white font-semibold rounded-lg transition-colors text-lg">
           Get Corrosion
-        </RouterLink>
+        </a>
       </div>
     </section>
   </div>