refactor: centralize action/icon button styles across all tools

Extract shared actionBtn and iconBtn constants into lib/utils/styles.ts
and replace all 11 local definitions across tool components.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/color/ColorManipulation.tsx

@@ -10,7 +10,7 @@ import { ExportMenu } from '@/components/color/ExportMenu';
 import { useColorInfo, useGeneratePalette, useGenerateGradient } from '@/lib/color/api/queries';
 import { Loader2, Share2, Plus, X, Palette, Layers } from 'lucide-react';
 import { toast } from 'sonner';
-import { cn } from '@/lib/utils';
+import { cn, actionBtn } from '@/lib/utils';
 import { MobileTabs } from '@/components/ui/mobile-tabs';
 
 type HarmonyType = 'monochromatic' | 'analogous' | 'complementary' | 'triadic' | 'tetradic';
@@ -32,8 +32,6 @@ const RIGHT_TABS: { value: RightTab; label: string }[] = [
   { value: 'gradient', label: 'Gradient' },
 ];
 
-const actionBtn =
-  'flex items-center gap-1 px-2.5 py-1 text-xs glass rounded-md border border-border/30 text-muted-foreground hover:text-primary hover:border-primary/30 hover:bg-primary/10 transition-all disabled:opacity-40 disabled:cursor-not-allowed';
 
 function ColorManipulationContent() {
   const searchParams = useSearchParams();