feat: add ico MIME type and heif->heic extension alias

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/mime.js

@@ -9,6 +9,7 @@ const OUTPUT_MIME_TYPES = {
   tiff: 'image/tiff',
   avif: 'image/avif',
   bmp: 'image/bmp',
+  ico: 'image/x-icon',
   pdf: 'application/pdf',
   html: 'text/html',
   txt: 'text/plain',
@@ -39,7 +40,9 @@ const UNDETECTABLE_TEXT_FORMATS = {
 };
 
 function normalizeFormat(format) {
-  return format === 'jpg' ? 'jpeg' : format;
+  if (format === 'jpg') return 'jpeg';
+  if (format === 'heif') return 'heic';
+  return format;
 }
 
 export async function resolveInputFormat(filePath, declaredFormat) {