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/FileConverter.tsx

@@ -17,13 +17,10 @@ import { addToHistory } from '@/lib/media/storage/history';
 import { downloadBlobsAsZip, generateOutputFilename } from '@/lib/media/utils/fileUtils';
 import type { ConversionJob, ConversionFormat, ConversionOptions } from '@/types/media';
 import { ShieldCheck, Download, RotateCcw, Loader2 } from 'lucide-react';
-import { cn } from '@/lib/utils';
+import { cn, actionBtn } from '@/lib/utils';
 
 type MobileTab = 'upload' | 'convert';
 
-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';
-
 const selectCls =
   'w-full bg-transparent border border-border/40 rounded-lg px-2.5 py-1.5 text-xs font-mono outline-none focus:border-primary/50 transition-colors text-foreground/80 cursor-pointer disabled:opacity-40';
 
@@ -439,7 +436,7 @@ export function FileConverter() {
                     <button
                       onClick={handleConvert}
                       disabled={!selectedFiles.length || !outputFormat || isConverting}
-                      className={cn(actionBtn, 'flex-1 py-2')}
+                      className={cn(actionBtn, 'flex-1 justify-center py-2')}
                     >
                       {isConverting
                         ? <><Loader2 className="w-3 h-3 animate-spin" />Converting…</>