fix: responsive C4 board on mobile and preserve chat input during morph

Shrink board cells to 36px with tighter gaps on <768px screens so the
board fits on 375px phones. Add DataIgnoreMorph to the C4 chat input
so typing isn't disrupted when new messages arrive.

assets/css/output.css

@@ -1723,6 +1723,18 @@
   .c4-chat-history {
     height: 150px;
   }
+  .board {
+    gap: 4px;
+    padding: 8px;
+  }
+  .column {
+    gap: 4px;
+    padding: 2px;
+  }
+  .cell {
+    width: 36px;
+    height: 36px;
+  }
 }
 .c4-chat {
   width: 100%;