feat(backend): implement custom services CRUD handlers

Add 6 admin endpoints for custom services: list (with search/popular/pagination), create, get, update, promote to regular service, and delete. Each handler validates admin role via middleware.

Ultraworked with Sisyphus (https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/main.go

@@ -291,6 +291,15 @@ func main() {
 				r.Delete("/{id}", admin.DeletePatchTest)
 			})
 
+			r.Route("/admin/custom-services", func(r chi.Router) {
+				r.Get("/", admin.GetCustomServices)
+				r.Post("/", admin.CreateCustomService)
+				r.Get("/{id}", admin.GetCustomService)
+				r.Put("/{id}", admin.UpdateCustomService)
+				r.Post("/{id}/promote", admin.PromoteCustomService)
+				r.Delete("/{id}", admin.DeleteCustomService)
+			})
+
 			r.Route("/admin/bookings", func(r chi.Router) {
 				r.Get("/", bookings.GetAllAdminBookingsHandler)
 				r.Post("/", bookings.AdminCreateBookingForUserHandler)