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/compose-settings.tsx

@@ -65,7 +65,7 @@ export function ComposeSettings() {
           id="compose-overlay-image"
           ref={overlayInputRef}
           type="file"
-          accept="image/*,.heic,.heif,.hif"
+          accept="image/*,.avif,.heic,.heif,.hif"
           onChange={(e) => setOverlayFile(e.target.files?.[0] ?? null)}
           className="hidden"
         />