fix: sidebar fills full grid cell height

Sidebar wrapper uses flex + h-full, .sidebar gets height: 100%,
removed min-height: 100vh (grid cell handles sizing).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/index.css

@@ -272,6 +272,7 @@
 
   .sidebar {
     min-height: 0;
+    height: 100%;
     overflow-y: auto;
   }