Removed `IDocReceiverElementWriter` interface and its implementation, replacing it with repository-based operations (`IRepository<DocReceiverElement>`). Updated `CreateEnvelopeCommandHandler` to use repository methods for deleting and creating `DocReceiverElement` records.
Cleaned up dependency injection by removing `IDocReceiverElementWriter` registration. Added new database triggers for `DocReceiverElement` in `appsettings.json` and `appsettings.Database.json`.
Introduced `SENDER_SAVE_EDIT_MIGRATION_PLAN.md` to outline the migration of the sender save/edit workflow to Blazor Server. This includes splitting save and send actions, supporting draft persistence, and enabling draft editing from the dashboard.
Removed unused namespaces and performed code cleanup. Updated testing strategies to ensure correctness and prevent regressions.
