IA-990: Fix: expose numeric ID endpoint on ChildController to unblock assistant resolution in recette
Context
AssistantResolverService and UserManagementServiceImpl both call /children/{userId} passing a numeric Long ID. ChildController only exposed UUID-based endpoints, causing a null lookup (findByUuid("42") → null) that worked locally but failed in recette.
Changes
- Added GET /children/numeric-id/{id} endpoint to ChildController
- Added getChildByNumericId(Long id) to ChildService and ChildServiceImpl
- Added GET_BY_NUMERIC_ID constant to ApiPaths
- Updated AssistantResolverService and UserManagementServiceImpl to call the new endpoint