5465: restore submit buttons when duplicate-item modal is dismissed

[mvanhorn]

Resolves #5465.

What

When the duplicate-item detection modal in audit_duplicates_controller opens, the form's submit buttons can already have been disabled and re-labelled "Saving" by Rails UJS (or another delegated handler that fires before the Stimulus submit listener gets to call preventDefault). Today, dismissing the modal via "Make Changes" or the close button never triggers a real form submission, so nothing restores those buttons — they stay disabled with the "Saving" label.

The existing fix in connect() (strip data-disable-with + data-remote) didn't fully cover this because:

• On Confirm Audit, the data-confirm flow can mark the button disabled as part of the re-dispatched click.
• Any future delegated handler that flips disabled on submit would slip past the attribute strip without us noticing.

How

showModal now snapshots each submit button's disabled flag and visible text when the modal opens. On hidden.bs.modal (single-use listener), if the user dismissed without going through mergeAndSubmit, restore the snapshotted values. The merge path is exempt because mergeAndSubmit actually submits the form and the page transitions away.

Verification

• Manual repro per the issue's steps: add two entries for the same item, click Save Progress, dismiss the modal — buttons are now interactive with their original labels.
• Same flow with Confirm Audit (clicking through the data-confirm prompt and then dismissing the duplicate modal).
• js: true audit-duplicates system spec at spec/system/audit_system_spec.rb:199 still exercises the merge path; the restore branch is the dismissal path so behaviour there is unchanged.
• No backend changes.

AI was used for assistance.