fix(StudioPage): move bottom spacing inside scroll container to prevent double scrollbar

The outer element had both a fixed height (`calc(100vh - marginTop)`) and
`margin-bottom: 16px`, making the total document height 16px taller than
the viewport. This caused the browser to show its own page-level scrollbar
alongside StudioPage's inner `overflow-y: auto` scroll.

Moving the spacing to `padding-bottom` on the inner element keeps it inside
the scrollable area so the document height stays at exactly 100vh.

Fixes #5864

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

Author: akolson

contentcuration/contentcuration/frontend/shared/views/StudioPage.vue

@@ -58,12 +58,12 @@
 
   .studio-page-outer {
     width: 100%;
-    margin-bottom: 16px;
     overflow-y: auto;
   }
 
   .studio-page-inner {
     width: 100%;
+    padding-bottom: 16px;
   }
 
 </style>