Devoluciones & RMA

POST /api/v1/returns — solicitar devolución
GET /api/v1/returns — listar (?filter[status]=requested)
GET /api/v1/returns/:id
PUT /api/v1/returns/:id/approve
PUT /api/v1/returns/:id/reject
PUT /api/v1/returns/:id/complete

Ciclo de estados: requested → approved → completed / requested → rejected