Add heir management functionality in Falukant module

- Implemented setHeir method in FalukantService to designate a child as heir, including validation checks for user and child relationships.
- Updated FalukantController to expose the setHeir endpoint, allowing users to set heirs via the API.
- Enhanced FalukantRouter with a new route for setting heirs.
- Modified FamilyView component to include UI elements for setting heirs, with success and error feedback.
- Updated localization files in both German and English to include new translations related to heir management, improving user experience.

backend/routers/falukantRouter.js

@@ -38,6 +38,7 @@ router.get('/director/:branchId', falukantController.getDirectorForBranch);
 router.get('/directors', falukantController.getAllDirectors);
 router.post('/directors', falukantController.updateDirector);
 router.post('/family/acceptmarriageproposal', falukantController.acceptMarriageProposal);
+router.post('/family/set-heir', falukantController.setHeir);
 router.get('/family/gifts', falukantController.getGifts);
 router.get('/family/children', falukantController.getChildren);
 router.post('/family/gift', falukantController.sendGift);