refactor: consolidate formations into trails

server/migrations/012_consolidate_learning_paths.sql

@@ -0,0 +1,5 @@
+-- Trilhas and Formações described the same object: an ordered collection of
+-- existing courses. Preserve every record while collapsing the duplicate type.
+update learning_paths set kind = 'trail' where kind = 'formation';
+drop index if exists learning_paths_kind_index;
+alter table learning_paths drop column kind;