feat(12.2-03): add hasMany relation contracts, relation forms and child create

- RelationContract gains Kind (empty is belongsToMany) and ForeignKey, with kind-aware boot checks
- manage.form, view.form and pivot.form compile against the related or pivot model; $/ paths resolve inside the plugin
- view toolbarButtons accept create|update|delete|link|unlink, each the capability of its routes
- POST .../relations/{name}/records creates a child through the manage form; the server sets the hasMany key
- relation schema carries kind, deferrable and the localized forms; 17 new relation message keys in en and pl

modules/cabana/admin_openapi.go

@@ -612,6 +612,29 @@ func AdminRelationLink() {}
 // @Router /{vendor}/{plugin}/{controller}/{id}/relations/{name}/unlink [post]
 func AdminRelationUnlink() {}
 
+// AdminRelationChildCreate documents the relation child create route.
+//
+// @Summary Create a related record
+// @Description Creates a record through the relation's manage form (manage.form, or the top-level form of config_relation.yaml) and attaches it to the owner: a hasMany child gets the owner's key in its foreign key (the server sets it; the body cannot), a belongsToMany record gets a pivot row. The view panel must declare the create toolbar button, otherwise 403. The owner is scoped like the record show route.
+// @Tags admin
+// @Accept json
+// @Produce json
+// @Security BackendBearer
+// @Param vendor path string true "Vendor"
+// @Param plugin path string true "Plugin"
+// @Param controller path string true "Controller"
+// @Param id path integer true "Owner id"
+// @Param name path string true "Relation name"
+// @Param body body AdminRecord true "Field values of the manage form keyed by field name"
+// @Success 201 {object} RecordEnvelope
+// @Failure 401 {object} ErrorEnvelope
+// @Failure 403 {object} ErrorEnvelope
+// @Failure 404 {object} ErrorEnvelope
+// @Failure 413 {object} ErrorEnvelope
+// @Failure 422 {object} ErrorEnvelope
+// @Router /{vendor}/{plugin}/{controller}/{id}/relations/{name}/records [post]
+func AdminRelationChildCreate() {}
+
 // FileMutationResult is the payload of a file removal: the number of files
 // removed (always 1 on success).
 type FileMutationResult struct {