Enhance branch management with foreign key relation handling

- Updated `BranchesModule` to include foreign key relations in list and write responses, ensuring they are represented as nested objects using `pickRelation`.
- Introduced new `relation-response.mdc` file to define guidelines for embedding foreign key relations.
- Modified `BranchesRepository` to support fetching related `division`, `createdByUser`, and `updatedByUser` data.
- Updated DTOs and service methods to reflect changes in response structure, removing direct foreign key IDs.
- Added unit tests to validate the new relation handling in branches service and repository.
- Enhanced e2e tests to verify the correct structure of branch responses with nested relations.

.cursor/rules/read-write-controllers.mdc

@@ -38,6 +38,7 @@ List requirements:
 - Shared pagination query (`page`/`limit` or `offset`/`limit`) via `PaginationQueryDto`
 - Handler **must** use `@Pagination()` and return `{ data, total }` — never build `meta` here (see `.cursor/rules/pagination-response.mdc`)
 - Service `visibleFields` whitelist: default **all non-secret** attributes; modules may narrow. Project in the **service**, not the controller
+- FK relations in list/detail (and write responses that reuse the mapper) MUST be nested objects via `pickRelation` — see `.cursor/rules/relation-response.mdc`
 - List query must be extendable (e.g. `extendListQuery(qb, filters)` on the repository/service) so joins/extra predicates can be added without forking list
 
 ## Write controller

.cursor/rules/relation-response.mdc

@@ -0,0 +1,33 @@
+---
+description: List/detail (and write responses that reuse the mapper) embed FK relations as objects via pickRelation
+globs: "src/modules/**/*.ts,src/common/http/response/**/*.ts"
+alwaysApply: false
+---
+
+# Relation Response Objects
+
+List, detail, and write handlers that reuse the same mapper MUST embed foreign keys as nested objects, not bare ids.
+
+## Field lists
+
+- Default catalog fields: `DEFAULT_RELATION_FIELDS` (`id`, `code`, `name`) from `src/common/http/response/`
+- Override per entity with a module/local constant (users: `USER_RELATION_FIELDS` = `id`, `username`)
+- Use `pickRelation(source, fields)` only — do not hand-roll partial copies
+
+## Mapping
+
+- Request DTOs still accept `*Id` (`divisionId`); the response key is the relation name (`division`, not `divisionId`)
+- Null FK → `null` (not omitted)
+- Never expose secrets (`passwordHash`, tokens) in relation objects
+- Load relations in the repository (joins or batch-load); map with `pickRelation` in the service
+
+```typescript
+// BAD
+return { divisionId: branch.divisionId, createdBy: branch.createdBy }
+
+// GOOD
+return {
+  division: pickRelation(branch.division, DEFAULT_RELATION_FIELDS),
+  createdBy: pickRelation(branch.createdByUser, USER_RELATION_FIELDS),
+}
+```