refactor: migrate remaining components to Design System v4

111 files across 14 directories: common, tree-editor, kb-accelerator,
copilot, assistant, analytics, library, procedural, procedural-editor,
public, script-editor, ui, admin, step-library.

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

frontend/src/components/common/Spinner.tsx

@@ -15,7 +15,7 @@ export function Spinner({ size = 'md', className }: SpinnerProps) {
   return (
     <div
       className={cn(
-        'animate-spin rounded-full border-border border-t-primary',
+        'animate-spin rounded-full border-[#1e2130] border-t-primary',
         SIZES[size],
         className
       )}