feat(12.1-02): password and form-only fields, rules per operation and preset

- pact.FormVirtualFields lists form fields that are not model columns: never
  bound, filled or projected; their values reach the Form hooks through
  cabana.VirtualFieldsFromContext when the field's context allows the operation
- type: password is a masked field that must be listed as virtual
- pact.FormRules supplies the rule set per operation and replaces the model's
  Rules() for admin saves; a rule on a virtual field sees the submitted value
- preset on a text field follows another text field on the create form
- SPA: PasswordField, preset handling in FormView, empty password left out of
  an update
- README, docs, OpenAPI document, TS types and dist updated

modules/cabana/relation.go

@@ -1131,7 +1131,7 @@ func (s RelationService) fillPivot(ctx context.Context, tx *gorm.DB, cr *Compile
 		return &CapabilityError{ControllerID: controllerID(form)}
 	}
 	rules := map[string]string{}
-	for key, rule := range mergedRules(form, pivot, "") {
+	for key, rule := range mergedRules(ctx, form, pivot, "") {
 		if slices.Contains(allowed, key) {
 			rules[key] = rule
 		}