fix: add .avif to all file picker accept strings

AVIF was missing from expandAccept() and every inline accept attribute,
causing the OS file picker to gray out .avif files. Drag-and-drop was
unaffected because it bypasses the accept filter. Added .avif to
dropzone.tsx expandAccept (covers all Dropzone pickers) plus 12 inline
accept strings across tool settings, pages, and file-upload-area.

apps/web/src/components/tools/meme-generator-preview.tsx

@@ -192,7 +192,7 @@ function TemplateGallery() {
         <input
           ref={fileInputRef}
           type="file"
-          accept="image/*,.heic,.heif,.hif"
+          accept="image/*,.avif,.heic,.heif,.hif"
           onChange={handleFileChange}
           className="hidden"
         />