- extend CreateEnvelopeCommand to support draft updates and send intent
- merge draft save logic into CreateEnvelopeCommandHandler and remove duplicate handler
- add DocReceiverElement writer abstraction and infrastructure registration for SQL-based field upserts
Introduced `UserPreferencesDto` to represent UI preferences,
including theme, dark mode, and grid layouts. Added the
`IUserPreferencesService` interface and implemented it in
`UserPreferencesService` to manage preferences stored in
the distributed cache (`dbo.TBDD_CACHE`).
Registered `UserPreferencesService` in dependency injection
and added a NuGet reference for `Microsoft.Extensions.Caching.Abstractions`.
Created `UserPreferencesController` with `GET` and `PUT`
endpoints to retrieve and save user preferences. Validated
theme names in the `PUT` endpoint.
Updated `Program.cs` to ensure proper service registration.
