feat(12.2-02): add the datepicker field with server-side bounds and date list columns

- type: datepicker compiles the D-20 keys; format maps to displayFormat with WinterCMS's momentFormat table
- boot fails when the mode does not match the column's Go type (time.Time, lagoon.Date, lagoon.TimeOfDay)
- datepicker is a writable scalar field; minDate and maxDate are rechecked on save
- columns.yaml accepts type: date and type: time; Scanner/Valuer structs are columns, not relations
- conformance fixture carries date and datetime fields; README, forms and lists docs

modules/cabana/crud.go

@@ -353,6 +353,12 @@ func (s CRUDService) save(ctx context.Context, cc *CompiledController, id any, i
 		if err != nil {
 			return &CapabilityError{ControllerID: controllerID(cc)}
 		}
+		for field, extra := range dateBoundDetails(ctx, s.tr, cc, target, op) {
+			if msgs == nil {
+				msgs = map[string][]string{}
+			}
+			msgs[field] = append(msgs[field], extra...)
+		}
 		if len(msgs) > 0 {
 			return &ValidationError{Details: validationDetails(msgs)}
 		}
@@ -812,7 +818,7 @@ func modelColumns(model any) map[string]struct{} {
 
 func scalarFormField(typ string) bool {
 	switch typ {
-	case "text", "textarea", "number", "checkbox", "switch", "dropdown":
+	case "text", "textarea", "number", "checkbox", "switch", "dropdown", "datepicker":
 		return true
 	default:
 		return false