fix: recipients with CC role not being editable (#918)

## Description

Fixed issue where setting a recipient role as CC will prevent any
further changes as it is considered as "sent" and "signed".

## Other changes

- Prevent editing document after completed
- Removed CC and Viewers from the field recipient list since they will
never be filled
- Minor UI issues

## Checklist

- [X] I have tested these changes locally and they work as expected.
- [X] I have added/updated tests that prove the effectiveness of these
changes.
- [X] I have followed the project's coding style guidelines.

packages/lib/server-only/field/set-fields-for-document.ts

@@ -46,6 +46,10 @@ export const setFieldsForDocument = async ({
     throw new Error('Document not found');
   }
 
+  if (document.completedAt) {
+    throw new Error('Document already complete');
+  }
+
   const existingFields = await prisma.field.findMany({
     where: {
       documentId,