fix: mobile-responsive layout for dashboard and board views

Add hamburger menu with off-canvas sidebar drawer on mobile.
Responsive padding, full-width panels, and stacked layouts
for screens under 768px (md breakpoint).

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

frontend/src/components/board-groups/BoardGroupsTable.tsx

@@ -130,7 +130,7 @@ export function BoardGroupsTable({
       stickyHeader={stickyHeader}
       emptyMessage={emptyMessage}
       rowClassName="transition hover:bg-slate-50"
-      cellClassName="px-6 py-4 align-top"
+      cellClassName="px-3 py-3 md:px-6 md:py-4 align-top"
       rowActions={
         showActions
           ? {