fix(dashboard): drop the border around the footer folder toggle

The status-bar folder-toggle button had a 1px border + radius that made it
look like a chip. Per request, render it as a bare icon — transparent
background, no border. Hover now only shifts the icon color, the active
state drops to color only, and focus-visible still draws a focus ring with
border-radius applied so it remains a clean halo.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/app/components/CustomModelDropdown.css

@@ -46,7 +46,7 @@
 
 .model-combobox-trigger-icon {
   display: inline-flex;
-  margin-right: 8px;
+  margin-right: var(--space-sm);
   flex-shrink: 0;
 }
 
@@ -160,6 +160,19 @@
   background: rgba(88, 166, 255, 0.25);
 }
 
+.model-combobox-option-main {
+  display: inline-flex;
+  align-items: center;
+  gap: var(--space-sm);
+  min-width: 0;
+  flex: 1;
+}
+
+.model-combobox-option-icon {
+  display: inline-flex;
+  flex-shrink: 0;
+}
+
 .model-combobox-option-text {
   flex: 1;
   overflow: hidden;