fix(nav): keep nav-item icon position constant across collapse

Collapsed nav-item now uses the same padding-based layout as the
expanded state, just clipped to the rail width. The icon sits at
the same x in both states so the rail no longer feels like the
items shift sideways during the transition.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: 2 people

app/globals.css

@@ -226,13 +226,13 @@ body.has-site-sidebar .site-content {
 }
 
 .sidebar:not(:hover):not(:focus-within) .nav-item {
-  width: 36px;
-  height: 36px;
-  min-height: 36px;
-  padding: 0;
-  margin: 0 auto;
+  height: 40px;
+  min-height: 40px;
+  width: calc(var(--sidebar-collapsed-width) - 24px);
+  padding: 0 11px;
+  margin: 0;
   gap: 0;
-  justify-content: center;
+  justify-content: flex-start;
   border-radius: 10px;
   overflow: hidden;
 }