Refine loading, disabled, success, and reset interactions in upload flow

[Alxandr]

Improve upload interaction states to prevent accidental duplicate actions and provide clear progress/success behavior.

Scope

• Disable submit and conflicting controls while upload is in flight.
• Keep loading state visible during upload.
• Standardize post-success reset/close behavior.

Acceptance Criteria

• Duplicate submissions are prevented while uploading.
• Users can clearly tell when upload is in progress.
• Success path consistently resets transient form state.