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/registry.go

@@ -96,6 +96,9 @@ func compileRegistry(items []controllerRef) (*Registry, error) {
 		if err := compileFileFields(item.plugin.ID(), compiled); err != nil {
 			return nil, err
 		}
+		if err := compileDateFields(item.plugin.ID(), compiled); err != nil {
+			return nil, err
+		}
 		if err := compileExtension(item.plugin.ID(), compiled, fsys.AdminFS()); err != nil {
 			return nil, err
 		}