feat: full admin theme expansion — spacing sliders, RGBA pickers, per-icon uploads

Admin Theme New Sections:
- 📐 Spacing & Layout: 9 range sliders for border-radius, content-max,
  header-h, nav-bottom-h, card-padding, section-gap, touch-min
- 🎲 Domino: 5 color pickers for game theming
- 🎯 Backgammon: 8 color pickers for board/checker/felt colors
- 🎨 Icons Grid: per-icon upload (31 icons individually replaceable)

RGBA Picker:
- Color input + alpha slider (0-100%) for rgba-based CSS variables
- Live preview, outputs rgba() string
- Applied to: board highlights, overlays, borders

Per-Icon Override:
- Individual SVG/PNG upload per icon
- Runtime: replaces SVG <use> with <img> element
- Resolution guide: "24×24px SVG مفضل"

Upload Resolution Guides:
- Pieces: 128×128px
- Logo: 200×40px
- Favicon: 32×32px
- Icons: 24×24px
- Sprite: SVG 24px viewBox

All changes live-effective via CSS variable injection + runtime JS.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

includes/footer.php

@@ -30,7 +30,21 @@ if (window.__themeAssets) {
         el.setAttribute('href', el.getAttribute('href').replace('/public/icons/sprite.svg', a['sprite-svg']));
       });
     }
+    // Individual icon overrides
     Object.keys(a).forEach(k => {
+      if (k.startsWith('icon-')) {
+        const iconName = k;
+        document.querySelectorAll('use[href$="#' + iconName + '"]').forEach(useEl => {
+          const svg = useEl.closest('svg');
+          if (svg) {
+            const img = document.createElement('img');
+            img.src = a[k];
+            img.style.cssText = 'width:100%;height:100%;object-fit:contain;';
+            img.alt = iconName;
+            svg.replaceWith(img);
+          }
+        });
+      }
       if (k.startsWith('piece-')) {
         const piece = k.replace('piece-', '');
         document.documentElement.style.setProperty('--piece-' + piece, 'url(' + a[k] + ')');

public/css/app.css

@@ -68,6 +68,10 @@
   --text-section: clamp(12px, 0.5vw + 10px, 14px);
   --text-body: clamp(13px, 0.5vw + 11px, 15px);
 
+  /* Spacing & Layout (admin-editable) */
+  --card-padding: 16px;
+  --section-gap: 16px;
+
   /* Board Theme — Chess.com green */
   --board-light: #EBECD0;
   --board-dark: #779556;