fix: remove max-width caps — board expands to fill all available space

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

public/css/backgammon.css

@@ -24,10 +24,10 @@
 /* ─── Game Layout ────────────────────────────────────────────────────────── */
 .bg-layout {
     display: flex;
-    gap: 16px;
+    gap: 12px;
     justify-content: center;
     align-items: flex-start;
-    max-width: 1300px;
+    max-width: 100%;
     margin: 0 auto;
     padding: 4px 8px;
     direction: ltr;
@@ -40,7 +40,6 @@
     align-items: center;
     flex: 1;
     min-width: 0;
-    max-width: 900px;
 }
 
 /* ─── Board Frame ────────────────────────────────────────────────────────── */
@@ -995,8 +994,8 @@
 
 /* ─── Responsive: Large screens ──────────────────────────────────────────── */
 @media (min-width: 1024px) {
-    .bg-board-column {
-        max-width: 1000px;
+    .bg-side-panel {
+        width: 220px;
     }
 
     :root {