[FEATURE]: Allow per-document configuration of signature workflow and visual effects

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

Currently in LibreSign, some behaviors such as:

• enabling/disabling confetti animation
• choosing sequential vs simultaneous signing workflow
  are configured only in the global application settings.

This means these options apply to all documents sent for signature, without the possibility to adjust them depending on the context of a specific document.

In practice, different documents may require different configurations.

Examples:

• Some contracts require sequential signing (one signer after another).
• Other documents work better with simultaneous signing.
• The confetti animation is nice in friendly contexts, but may be inappropriate for formal, legal, or administrative documents.

Because these options are global, administrators must choose a single configuration that may not fit all use cases.

Describe the solution you'd like

Add the possibility to configure these options at the document request level, when creating a new signature request.

For example, when sending a document for signature, allow the sender to define:

Signature workflow

• Sequential signing
• Simultaneous signing

Visual effects

• Enable confetti
• Disable confetti

These settings would override the global configuration only for that specific document.

The global settings would remain the default behavior.

Describe alternatives you've considered

Currently the only workaround is to modify the global settings of LibreSign before sending a specific document.

However this is not practical because:

• it affects all other documents
• it requires administrators to constantly change system settings
• it introduces risk of sending documents with the wrong workflow configuration

Another workaround would be to maintain multiple LibreSign instances with different configurations, but this is clearly excessive for such a simple need.

Additional context

At this stage, I am already able to use LibreSign effectively and this feature is not a critical requirement for my current workflows.

However, I strongly believe LibreSign has the potential to become a powerful catalyst for Nextcloud adoption. Electronic signature is a highly visible and strategic feature that can attract new users and organizations to the Nextcloud ecosystem.

Being able to offer flexibility similar to other signature platforms would make LibreSign even more compelling when presenting Nextcloud as a complete alternative to proprietary collaboration tools.

In that sense, features like this would help promote LibreSign and strengthen its appeal, especially when introducing the tool to new users or organizations considering adopting Nextcloud.

Start by tracing how a new signature request reads global settings and how the signing workflow and confetti effect consume them. Define the request-level options and verify that they override global values for one document while leaving global settings as defaults when unset.