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/variables.css

@@ -0,0 +1,24 @@
+:root {
+  /* Theme defaults (overridden per site via inline style) */
+  --bg: #0a0a0c;
+  --bg-elevated: #111115;
+  --bg-card: #16161b;
+  --text: #e8e8ed;
+  --text-dimmed: #6e6e7a;
+  --accent: #c9a84c;
+  --accent-light: rgba(201, 168, 76, 0.1);
+
+  /* Layout */
+  --max-width: 700px;
+  --radius: 8px;
+  --spacing-xs: 4px;
+  --spacing-sm: 8px;
+  --spacing-md: 16px;
+  --spacing-lg: 24px;
+  --spacing-xl: 48px;
+
+  /* Typography */
+  --font-primary: Inter, -apple-system, BlinkMacSystemFont, sans-serif;
+  --font-secondary: Inter, sans-serif;
+  --font-mono: 'SF Mono', 'Fira Code', 'Cascadia Code', monospace;
+}