fix: quick access panel buttons overflow when bottom panel is small

Add overflow-y: auto to .default-panel-content so buttons scroll
instead of spilling into the editor area. Replace justify-content:
center with margin-top/bottom: auto on heading/buttons to keep
vertical centering when space allows while staying scrollable when
it does not.

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

Author: 2 people

src/styles/Extn-BottomPanelTabs.less

@@ -354,11 +354,11 @@
     display: flex;
     flex-direction: column;
     align-items: center;
-    justify-content: center;
     height: 100%;
     padding: 16px;
     gap: 12px;
     user-select: none;
+    overflow-y: auto;
 }
 
 .default-panel-heading {
@@ -367,7 +367,9 @@
     word-spacing: 1px;
     font-weight: 500;
     color: #555;
+    margin-top: auto;
     margin-bottom: 4px;
+    flex-shrink: 0;
 
     .dark & {
         color: #bbb;
@@ -379,6 +381,8 @@
     flex-wrap: wrap;
     justify-content: center;
     gap: 8px;
+    margin-bottom: auto;
+    flex-shrink: 0;
 }
 
 .default-panel-btn {