getStorageControllers() was looking at ROOT/storage-controllers but the
actual files live at ROOT/src/storage-controllers — so all 3 storage
backends (S3, FTP, alt-folder) silently failed to load at runtime.

Also rename FTPStorage to FtpStorage to match the loader's ucfirst
convention; the all-caps name never matched and would have caused a
class-not-found error once discovery worked.