refactor: replace hardcoded hex values with Tailwind semantic tokens

3,200+ hardcoded color values replaced with CSS variable-backed
Tailwind classes (bg-card, text-foreground, border-border, etc.).
Enables light mode via CSS variable swap. Only syntax highlighting
colors and intentional one-offs remain hardcoded (~15 values).

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

frontend/src/components/library/SortDropdown.tsx

@@ -21,7 +21,7 @@ const sortOptions: { value: SortBy; label: string }[] = [
 export function SortDropdown({ value, onChange, className }: SortDropdownProps) {
   return (
     <div className={cn('relative inline-flex items-center', className)}>
-      <span className="mr-2 flex items-center gap-1.5 text-sm text-[#848b9b]">
+      <span className="mr-2 flex items-center gap-1.5 text-sm text-muted-foreground">
         <ArrowUpDown className="h-4 w-4" />
         <span className="hidden sm:inline">Sort:</span>
       </span>
@@ -29,8 +29,8 @@ export function SortDropdown({ value, onChange, className }: SortDropdownProps)
         value={value}
         onChange={(e) => onChange(e.target.value as SortBy)}
         className={cn(
-          'rounded-md border border-[#1e2130] bg-[#14161d] px-3 py-1.5 text-sm',
-          'text-[#e2e5eb] focus:border-primary focus:outline-hidden focus:ring-1 focus:ring-primary/20'
+          'rounded-md border border-border bg-card px-3 py-1.5 text-sm',
+          'text-foreground focus:border-primary focus:outline-hidden focus:ring-1 focus:ring-primary/20'
         )}
       >
         {sortOptions.map((option) => (