Require at least one signature field before sending document

Is your feature request related to a problem? Please describe.

As a document creator in LibreSign, I can send a document to a
signer without placing any signature fields. This leads to confusion
for the recipient, who receives a document but has no idea where
or whether they need to sign.

Describe the solution you'd like

LibreSign should validate before sending a document that at least
one signature field has been placed. If no signature field exists,
the send button should be disabled or a warning message should
appear, preventing the document from being sent without a
designated signing area.

Describe alternatives you've considered

Currently the only alternative is an internal policy reminding
creators to always place signature fields manually. This is
error-prone and not a reliable solution, especially for teams
with multiple users.

Additional context

This would significantly improve the user experience for both
document creators and recipients. It is a common validation
feature in other signing tools like DocuSign or Adobe Sign and
would make LibreSign more professional and reliable for
business use.

Start by tracing the document-send flow and the send button's handling of placed signature fields. Verify how the interface detects whether any signature field exists, then confirm that a document with none cannot be sent and that the warning or disabled state is clear to the creator.