SceneElement gains enabled/clickable/selected/checked/focused (bool | None),
populated from the literal attributes Appium's XCUITest and UiAutomator2
page_source already emit (iOS: enabled only; Android: all five). None means
"not reported by this platform", not false. to_dict() omits unset fields to
keep the LLM-facing scene JSON compact; planner_prompts.py documents the new
fields so the AI planner knows how to use them (e.g. don't tap disabled
elements, use selected/checked to judge whether a toggle already matches the
goal).
