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/contracts.go

@@ -102,6 +102,9 @@ type CompiledController struct {
 	// dates are the form's `type: datepicker` fields after the Go type
 	// check, keyed by field name.
 	dates map[string]*compiledDate
+	// virtual is the set of form field names the controller lists through
+	// pact.FormVirtualFields: never bound, filled or projected.
+	virtual map[string]bool
 }
 
 // Registry is the immutable controller map keyed by controller ID.