The `uploading` flag was only cleared by `x-init="uploading = false"` on the
file list, which Alpine runs when the element is initialized. Adding a second
batch of files to the same share only patches that existing element, so the
flag stayed true forever: the spinner never went away, the drop zone stayed
disabled and the submit button stayed disabled, making the share impossible
to create.
`updatedFiles()` now dispatches `files-processed`, which runs for every batch,
and the form resets its upload state on that event instead.
Also fixes two adjacent bugs in the drag & drop path: `uploadMultiple()` was
called without callbacks so dropped files showed no progress at all, and
`relativePaths` was replaced instead of appended, shifting every earlier
file's path onto the wrong file on a second drop.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
