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/media/ConversionPreview.tsx

@@ -2,7 +2,7 @@
 
 import * as React from 'react';
 import { Download, CheckCircle, XCircle, Loader2, Clock, TrendingUp, RefreshCw } from 'lucide-react';
-import { cn } from '@/lib/utils/cn';
+import { cn, actionBtn } from '@/lib/utils';
 import { downloadBlob, formatFileSize, generateOutputFilename } from '@/lib/media/utils/fileUtils';
 import type { ConversionJob } from '@/types/media';
 
@@ -11,9 +11,6 @@ export interface ConversionPreviewProps {
   onRetry?: () => void;
 }
 
-const actionBtn =
-  'flex items-center justify-center gap-1.5 px-3 py-1.5 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 ConversionPreview({ job, onRetry }: ConversionPreviewProps) {
   const [previewUrl, setPreviewUrl] = React.useState<string | null>(null);
   const [elapsedTime, setElapsedTime] = React.useState(0);
@@ -171,7 +168,7 @@ export function ConversionPreview({ job, onRetry }: ConversionPreviewProps) {
           })()}
 
           {/* Download */}
-          <button onClick={handleDownload} className={cn(actionBtn, 'w-full')}>
+          <button onClick={handleDownload} className={cn(actionBtn, 'w-full justify-center')}>
             <Download className="w-3 h-3" />
             <span className="truncate min-w-0">{filename}</span>
           </button>
@@ -187,7 +184,7 @@ export function ConversionPreview({ job, onRetry }: ConversionPreviewProps) {
             </div>
           )}
           {onRetry && (
-            <button onClick={onRetry} className={cn(actionBtn, 'w-full')}>
+            <button onClick={onRetry} className={cn(actionBtn, 'w-full justify-center')}>
               <RefreshCw className="w-3 h-3" />
               Retry
             </button>