US-10 — Save a notification as a draft

## User story

As a notification author, I want to save an unfinished notification as a draft so that I can complete it later.

## Acceptance scenarios

```gherkin
Feature: Save a notification as a draft

Background:
Given the author is composing a notification

Scenario: Save a complete notification as a draft
When the author saves the notification as a draft
Then the notification should be stored
And its status should be "draft"

Scenario: Save an incomplete notification as a draft
Given some dispatch-required fields are incomplete
When the author saves the notification as a draft
Then the notification should be stored
And its status should remain "draft"
And it should not be dispatched or scheduled

Scenario: Record the draft author
When the notification is saved as a draft
Then the current author should be recorded as the last author
And the last modified date and time should be recorded
```

No files or tests are named in the issue. Start by locating the existing notification save and dispatch or scheduling entry points, then trace how status, author, and modification time are persisted. Done means complete and incomplete notifications can be stored as drafts without dispatch or scheduling, with the current author and modification time recorded.

Written by the indexing model from the issue text.