chore(server): use native file-type implementation (#6686)

packages/backend/native/index.d.ts

@@ -1,6 +1,8 @@
 /* auto-generated by NAPI-RS */
 /* eslint-disable */
 
+export function getMime(input: Uint8Array): string
+
 /**
  * Merge updates in form like `Y.applyUpdate(doc, update)` way and return the
  * result binary.