feat: initial mono-repo with 30 vanity domain sites

Scaffold complete repo structure:
- 28 static sites extracted from running containers on mlake
- 2 dynamic sites (dasbes.de, dumusst.com) marked for separate handling
- Template system with 6 templates (person-dark/light, product-dark, editorial, fun, minimal)
- Shared CSS (variables, responsive, animations, noise overlay)
- nginx config generator with multi-domain alias support
- Build script with Docker-based nginx validation
- add-site.sh helper for scaffolding new domains
- Dockerfile for single nginx:alpine container

Sites: clemensplassmann.de, danosi.de, deinesei.de, derkaiseristnackt.de,
elefantenhor.de, fragina.de, frenchkis.de, ichbinaufbali.de, ichbinaufbarley.de,
insain.de, julietensity.de, kainco.de (+keinco.de), kainstress.de, keinefreun.de,
knzlmgmt.de, kopffrai.de, legalais.de, machesdocheinfach.de, mai-otto.de
(+otto.flexsiebels.de, ottomatisch.de, ichbinotto.de), martinsiebels.de,
matthiasbreier.de, osterai.de, paragraphenraiter.de, schulfrai.de, smartin3.de,
sorgenfrai.de, vonschraitter.de, wartebitte.de

Refs: otto#341

shared/css/responsive.css

@@ -0,0 +1,45 @@
+*, *::before, *::after {
+  box-sizing: border-box;
+  margin: 0;
+  padding: 0;
+}
+
+html {
+  font-size: 16px;
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+}
+
+body {
+  font-family: var(--font-primary);
+  background: var(--bg);
+  color: var(--text);
+  line-height: 1.6;
+  min-height: 100vh;
+}
+
+.container {
+  max-width: var(--max-width);
+  margin: 0 auto;
+  padding: var(--spacing-xl) var(--spacing-lg);
+}
+
+@media (max-width: 768px) {
+  .container {
+    padding: var(--spacing-lg) var(--spacing-md);
+  }
+
+  .grid {
+    grid-template-columns: 1fr !important;
+  }
+}
+
+@media (max-width: 640px) {
+  html {
+    font-size: 15px;
+  }
+
+  .container {
+    padding: var(--spacing-md) var(--spacing-sm);
+  }
+}