Draft events disable 'publish to ATProto' checkbox and can't re-enable

[tompscanlan]

Summary

When saving an event as a draft, the "Publish to ATProtocol" checkbox automatically gets unchecked and cannot be re-enabled afterwards. This makes drafts incompatible with ATProtocol functionality.

Steps to Reproduce

1. Log in as an ATProtocol-connected user
2. Create a new event
3. Check "Publish to ATProtocol"
4. Save the event as a draft
5. Observe: The "Publish to ATProtocol" checkbox is now unchecked
6. Try to re-check it - the checkbox cannot be enabled

Expected Behavior

• Either allow re-enabling the ATProto checkbox on draft events
• Or preserve the user's ATProto preference when saving as draft

Actual Behavior

• Saving as draft permanently disables ATProto publishing for that event
• Users cannot recover from this state

Context

Discovered during PR #449 testing. Lower priority than the location schema fix but should be addressed for ATProto users who want to draft events before publishing.

Related: OpenMeet-Team/openmeet-api#449