Fix: Add runtime validation for _correctRange values (fixes #231)

[swashbuck]

Fixes #231

Fix

• Add validateCorrectRange() method to SliderModel that runs during init(), before setupModelItems()
• Detect and correct invalid _correctRange configurations with console warnings:
  • Inverted range (_bottom > _top) - values are swapped
  • Out-of-bounds values - clamped to _scaleStart/_scaleEnd
  • Misaligned step values - snapped to nearest valid _scaleStep increment

Testing

1. Configure a Slider with an inverted range (e.g. _bottom: 9, _top: 4) - verify console warning and correct scoring
2. Configure with out-of-bounds values (e.g. _bottom: 50 on a scale ending at 10) - verify clamping and warning
3. Configure with step-misaligned values (e.g. _bottom: 3 with _scaleStep: 2 starting at 1) - verify snapping to nearest step
4. Verify normal valid ranges still work without warnings
5. Verify _correctAnswer mode is unaffected (validation skips when _correctAnswer is set)

Performance Impact

None - validation runs once during init() with O(1) operations