feat: add 'Correct signature' button to reset a signer and re-request their signature

[VictorSandovalDev]

Adds an admin-facing "Correct signature" button on completed submitters in the submission view, for cases where a signature was made incorrectly and needs to be redone.

What it does

When an authorized user clicks the button on a completed submitter, it:

1. Clears that submitter's existing signature (documents, attachments and field values)
2. Reopens their form (resets completed_at / opened_at)
3. Re-sends the invitation email so they can sign again

Unlike the existing resubmit flow (which is limited to submitter.email == current_user.email and clones the whole submission), this works in place on the same submission — which matters for multi-signer documents where all recipients share one document.

Changes

• New SubmittersResetSignatureController#update (authorized via can?(:update, submitter))
• New route resources :submitters_reset_signature, only: [:update]
• Button in submissions/show.html.erb, shown for completed submitters when the user can update the submission (with a confirmation prompt)
• EN/ES i18n strings

Notes

• Reuses the existing SendSubmitterInvitationEmailJob for the email.
• The action is guarded so it only runs on already-completed submitters.

Feedback welcome on naming and whether this should be gated behind an account setting.