Fix: Show full correct range and improve post-submit slider state (fixes #184)

[swashbuck]

Fixes #184

Fix

1. Number range: When a range-based slider is answered correctly, the full correct range is now shown. Previously, only the learner's single chosen value was indicated. _canShowModelAnswer must be true.

2. Visible thumb after submission: The slider thumb now stays visible after a correct submit (marks the learner's pick). It is hidden only during the "show correct answer" view for an incorrect submission. is-disabled keeps cursor: default to signal the control is non-interactive.

3. Fill bar issue: Fixed the fill bar during "show correct answer": it now spans the actual correct range instead of running from the scale start to the range midpoint. Previously a 5-9 range highlighted 5-9 but filled 1-7, which was misleading.

Previous:

Fixed:

4. Correct-range colour: The widget now adds the show-correct-answer class whenever the correct range is shown (including on a correct submit), so the existing Vanilla theme rules colour the range circles and fill with the validation/success colour. No companion theme change required. The thumb-hide rule was scoped to .show-correct-answer.is-incorrect so the thumb stays visible on a correct submit.

Testing

1. Use a slider with a _correctRange (e.g. _bottom: 5, _top: 9) and _canShowModelAnswer: true.
2. Answer correctly (e.g. 7) and submit. Expect: the full 5-9 range is highlighted in the validation/success colour, the thumb stays visible at your chosen value, and the fill runs to your value.
3. Reset, answer incorrectly (e.g. 2) and submit, then select "Show correct answer". Expect: the 5-9 range is highlighted, no thumb is shown, and the fill spans 5-9 (not 1-7).
4. Toggle "Show your answer" / "Show correct answer" and confirm the views switch correctly.

Companion issue to create

Hiding the handle in Confidence Slider - adapt-contrib-confidenceSlider extends SliderView and reuses the same slider__widget / slider__item markup, so it shares slider's compiled thumb CSS. Because confidenceSlider never applies show-correct-answer, the changes here leave its handle visible after submit (it was previously hidden). If we want to retain the previous behaviour, confidenceSlider should add its own thumb-hide rule or be updated to decouple from slider's .show-correct-answer gating.

After submit:

Posted via collaboration with Claude Code