GitLab returns null for the label/milestone fields on resource_label_events
and resource_milestone_events when the referenced label or milestone has
been deleted. This caused deserialization failures during sync.
- Add migration 012 to recreate both event tables with nullable
label_name, milestone_title, and milestone_id columns (SQLite
requires table recreation to alter NOT NULL constraints)
- Change GitLabLabelEvent.label and GitLabMilestoneEvent.milestone
to Option<> in the Rust types
- Update upsert functions to pass through None values correctly
- Add tests for null label and null milestone deserialization
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
