feat(KB-654): add dynamic viewport height for mobile board layout

- Add 100dvh fallback after 100vh for proper mobile browser chrome handling
- Fixes board overflow issues on mobile Safari/Chrome where dynamic toolbars affect viewport
- Maintains backward compatibility with 100vh for older browsers

packages/dashboard/app/styles.css

@@ -382,6 +382,7 @@ body {
   gap: var(--column-gap);
   padding: var(--board-padding);
   height: calc(100vh - 57px);
+  height: calc(100dvh - 57px);
   overflow-x: auto;
   overflow-y: hidden;
   scroll-snap-type: x proximity;