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

build.sh

@@ -0,0 +1,59 @@
+#!/bin/bash
+# Build all sites: generate nginx.conf, render templates, prepare build/ directory
+set -euo pipefail
+
+SCRIPT_DIR=$(cd "$(dirname "$0")" && pwd)
+BUILD_DIR="$SCRIPT_DIR/build"
+
+echo "=== Onepager Build ==="
+
+# Clean build directory
+rm -rf "$BUILD_DIR"
+mkdir -p "$BUILD_DIR"
+
+# 1. Generate nginx.conf
+echo "[1/3] Generating nginx.conf..."
+"$SCRIPT_DIR/nginx/generate-nginx.sh" "$SCRIPT_DIR/sites" > "$SCRIPT_DIR/nginx/nginx.conf"
+echo "  -> nginx/nginx.conf written"
+
+# 2. Build each site
+echo "[2/3] Building sites..."
+count=0
+for site_dir in "$SCRIPT_DIR/sites"/*/; do
+    [ -f "$site_dir/site.yaml" ] || continue
+    domain=$(basename "$site_dir")
+    template=$(yq -r '.template // "custom"' "$site_dir/site.yaml")
+
+    mkdir -p "$BUILD_DIR/$domain"
+
+    if [ "$template" = "custom" ]; then
+        # Copy everything except site.yaml
+        find "$site_dir" -maxdepth 1 -not -name site.yaml -not -path "$site_dir" -exec cp -r {} "$BUILD_DIR/$domain/" \;
+        echo "  [custom] $domain"
+    else
+        template_file="$SCRIPT_DIR/templates/${template}.html"
+        if [ ! -f "$template_file" ]; then
+            echo "  [ERROR] Template '$template' not found for $domain — skipping" >&2
+            continue
+        fi
+        "$SCRIPT_DIR/render.sh" "$site_dir/site.yaml" "$template_file" > "$BUILD_DIR/$domain/index.html"
+        # Copy assets if present
+        [ -d "$site_dir/assets" ] && cp -r "$site_dir/assets" "$BUILD_DIR/$domain/"
+        echo "  [${template}] $domain"
+    fi
+    count=$((count + 1))
+done
+echo "  -> $count sites built"
+
+# 3. Validate nginx config (if docker is available)
+echo "[3/3] Validating nginx config..."
+if command -v docker &>/dev/null; then
+    docker run --rm \
+        -v "$SCRIPT_DIR/nginx/nginx.conf:/etc/nginx/nginx.conf:ro" \
+        -v "$BUILD_DIR:/usr/share/nginx/html:ro" \
+        nginx:alpine nginx -t 2>&1 && echo "  -> nginx config valid" || echo "  [WARN] nginx validation failed (non-fatal for local builds)"
+else
+    echo "  [SKIP] Docker not available, skipping nginx validation"
+fi
+
+echo "=== Build complete: $count sites ==="