feat(#205): renommer absences_garde → evenements_agenda

Migration live + BDD.sql from-scratch, module Nest / API
/evenements-agenda, FK cartes id_evenement. Front stub path aligné.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/src/modules/evenements-agenda/index.ts

@@ -0,0 +1,2 @@
+export { EvenementsAgendaModule } from './evenements-agenda.module';
+export { EvenementsAgendaService } from './evenements-agenda.service';