FormControlState cannot express an unread checked/selected state #103

Found in the review of the capture-live-form-state branch.

FormControlState.checked / selected are Booleans defaulting to false, so a capture that did not read them removes the markup's checked / selected (for value, null means "keep the markup").

Scenario: the CDP capture turns a missing inputChecked / optionSelected rare-data field into an empty set (?.index.toIndexSet()).
If a Chrome version or a snapshot omits the field, every <input type=checkbox checked> and <option selected> loses its state and the dump shows every box unticked.
A future caller building FormControlState(value = …) without the flags hits the same thing.

Fix: make both Boolean? with null = keep the markup, and have CapturePage pass null when the rare data is absent.