fix: reduce version text size and increase separation from brand name

Version in sidebar header now 10px (was 12px), 8px margin (was 4px),
with reduced opacity for visual hierarchy.

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

src/design-system/layout/Sidebar/Sidebar.module.css

@@ -70,9 +70,10 @@
 
 .version {
   font-family: var(--font-mono);
-  font-size: 12px;
+  font-size: 10px;
   color: var(--sidebar-muted);
-  margin-left: 4px;
+  margin-left: 8px;
+  opacity: 0.6;
 }
 
 /* Search */