feat: apply B-147 visual tokens to shell and three representative pages

Closes B-156

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: multica-agent <github@multica.ai>

app/frontend/shared/components/navigation.css

@@ -52,21 +52,21 @@
 }
 
 .segmented {
-  height: 34px;
+  height: var(--control-height);
 
   display: flex;
 
   overflow: hidden;
 
-  min-height: 36px;
+  min-height: var(--control-height);
 
   padding: 2px;
 
   border: 0px;
 
-  border-radius: 7px;
+  border-radius: var(--radius-md);
 
-  background: rgb(236, 239, 244);
+  background: var(--surface-muted);
 }
 
 .segment {
@@ -82,11 +82,11 @@
 
   border: 0px;
 
-  border-radius: 5px;
+  border-radius: 6px;
 
   color: var(--text-secondary);
 
-  font-size: 11.5px;
+  font-size: var(--font-size-label);
 }
 
 .segment.active {