fix: prevent left-side clipping on large boards

Replace flex centering on scroll container with margin auto on the
board element so overflowing boards remain fully scrollable.

src/views/Board.svelte

@@ -96,6 +96,7 @@
         border-radius: var(--radius);
         overflow: hidden;
         background: var(--bg-deep);
+        margin: 0 auto;
     }
 
     .floor,

src/views/GameView.svelte

@@ -196,8 +196,6 @@
     }
 
     .board-wrap {
-        display: flex;
-        justify-content: center;
         width: 100%;
         overflow: auto;
         max-height: calc(100vh - 140px);