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/qrcode/QRPreview.tsx

@@ -1,7 +1,7 @@
 'use client';
 
 import { Copy, Share2, Image as ImageIcon, FileCode, QrCode } from 'lucide-react';
-import { cn } from '@/lib/utils/cn';
+import { cn, actionBtn } from '@/lib/utils';
 import type { ExportSize } from '@/types/qrcode';
 
 interface QRPreviewProps {
@@ -22,8 +22,6 @@ const EXPORT_SIZES: { value: ExportSize; label: string }[] = [
   { value: 2048, label: '2k' },
 ];
 
-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';
 
 export function QRPreview({
   svgString,