Agent Skills: mx-pg-controller-migration

Use when verifying and porting an mx-core controller (Post/Note/Page/Comment/Category/etc.) after the MongoDB→PostgreSQL cutover, or when its data shape no longer matches what api-client and admin-vue3 expect. Triggers on "校验 controller"、"check controller"、"迁移 controller"、"修复迁移后的接口"、"data missing after PG migration"、"related/category 字段丢了" and similar.