[FEATURE]: Multiple signatures

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

Currently 1 user can have only 1 signature. Imagine you are director of a company. Sometimes you have to sign private documents with your uploaded hand signature, sometimes you have to sign internal documents like purchase orders where a simple Text is sufficient, and sometimes you have to sign legally binding contract with your hand signature and the company seal. Seems this is currently impossible.

Describe the solution you'd like

The Account page already shows heading "Your signatures" implying multiple signatures could be added. But currently it allows only for one signature. Here could be a list or a drop-down menu to add multiple signature.

Describe alternatives you've considered

No response

Additional context

No response

Start at the Account page and trace the existing single-signature flow through the project. Clarify how signatures are added, stored, and selected, then define the UI and behavior for adding and choosing multiple signatures; done means users can use distinct uploaded or text signatures for different documents.