Migrate insight creation to the command system with automatic retry logic
to prevent SurrealDB transaction conflicts during batch imports.
Changes:
- Add create_insight_command with retry logic for transaction conflicts
- Add run_transformation_command for async transformation execution
- Make Source.add_insight() fire-and-forget (returns command_id)
- Update POST /sources/{id}/insights to return 202 Accepted immediately
- Frontend polls command status until complete, then refreshes
- Auto-update notebook page icon when source gains insights
- Add i18n keys for insight generation feedback
Related to #489
301dd4e20a