Initial commit: Site Builder with PHP API backend

Visual drag-and-drop website builder using GrapesJS with:
- Multi-page editor with live preview
- File-based asset storage via PHP API (no localStorage base64)
- Template library, Docker support, and Playwright test suite

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

templates/thumbnails/portfolio-designer.svg

@@ -0,0 +1,26 @@
+<svg width="400" height="260" xmlns="http://www.w3.org/2000/svg">
+  <defs>
+    <linearGradient id="bg-portfolio-designer" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#1c1917"/>
+      <stop offset="100%" style="stop-color:#f97316"/>
+    </linearGradient>
+  </defs>
+  <rect width="400" height="260" rx="12" fill="url(#bg-portfolio-designer)"/>
+  <!-- Nav bar -->
+  <rect x="0" y="0" width="400" height="32" rx="12" fill="rgba(0,0,0,0.3)"/>
+  <rect x="12" y="10" width="60" height="12" rx="3" fill="#f97316" opacity="0.8"/>
+  <rect x="280" y="10" width="40" height="12" rx="3" fill="rgba(255,255,255,0.2)"/>
+  <rect x="330" y="10" width="40" height="12" rx="3" fill="rgba(255,255,255,0.2)"/>
+  <!-- Hero text lines -->
+  <rect x="40" y="70" width="200" height="18" rx="4" fill="rgba(255,255,255,0.9)"/>
+  <rect x="40" y="96" width="160" height="10" rx="3" fill="rgba(255,255,255,0.3)"/>
+  <rect x="40" y="112" width="180" height="10" rx="3" fill="rgba(255,255,255,0.3)"/>
+  <!-- CTA button -->
+  <rect x="40" y="136" width="100" height="28" rx="6" fill="#f97316"/>
+  <!-- Content blocks -->
+  <rect x="40" y="185" width="100" height="50" rx="6" fill="rgba(255,255,255,0.08)"/>
+  <rect x="150" y="185" width="100" height="50" rx="6" fill="rgba(255,255,255,0.08)"/>
+  <rect x="260" y="185" width="100" height="50" rx="6" fill="rgba(255,255,255,0.08)"/>
+  <!-- Accent circle -->
+  <circle cx="340" cy="90" r="40" fill="#fafaf9" opacity="0.15"/>
+</svg>