Fix Critical Issues: Mobile Scrolling, Auto Mode Crash, and Enhanced Robustness

Summary

This PR addresses three critical issues in the vue3-carousel component:

1. Issue Cannot scroll vertically to other section in mobile view. #525: Mobile vertical scrolling blocked - Fixed by changing touch event passive flag to allow native browser scrolling
2. Issue Carousel breaks page #524: Carousel crashes with itemsToShow: 'auto' - Fixed by adding safety guards and iteration limits to prevent infinite loops
3. Enhanced robustness - Improved calculateAverage utility with better input validation

The changes are targeted and focused on the specific root causes identified in each issue, with comprehensive test coverage maintained.

Review & Testing Checklist for Human

⚠️ Critical items to verify (medium risk):

• Test mobile scrolling on actual touch device - Verify that vertical page scrolling works properly while horizontal carousel dragging still functions
• Test auto mode with various configurations - Set itemsToShow: 'auto' and verify no crashes occur with different slide counts and sizes
• Verify no regressions in normal carousel behavior - Test standard carousel functionality (navigation, pagination, dragging) to ensure existing features still work
• Check infinite loop protection doesn't trigger incorrectly - Test edge cases where slides have zero/invalid dimensions to ensure safety guards work appropriately

Recommended test plan:

1. Run the development playground (pnpm dev) and test mobile scrolling in browser dev tools mobile mode
2. Test itemsToShow: 'auto' with different slide configurations
3. Deploy to a test environment and verify mobile scrolling on actual devices
4. Run full test suite to ensure no regressions

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    useDrag["src/composables/useDrag.ts<br/>Touch event handling"]:::major-edit
    Carousel["src/components/Carousel/Carousel.ts<br/>Main carousel logic"]:::major-edit
    calculateAverage["src/utils/calculateAverage.ts<br/>Number validation utility"]:::minor-edit
    
    touchEvents["Touch Events<br/>(touchstart, touchmove)"]:::context
    autoMode["Auto Mode<br/>(itemsToShow: 'auto')"]:::context
    visibleRange["visibleRange computation<br/>Slide positioning"]:::context
    
    useDrag -.->|"passive: isTouch"| touchEvents
    Carousel -.->|"safety guards"| autoMode
    Carousel -.->|"iteration limits"| visibleRange
    calculateAverage -.->|"isFinite() validation"| Carousel
    
    subgraph Legend
        L1[Major Edit]:::major-edit
        L2[Minor Edit]:::minor-edit  
        L3[Context/No Edit]:::context
    end
    
    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB
    classDef context fill:#FFFFFF

Notes

• All 101 tests pass with no regressions
• The mobile scrolling fix changes the passive flag from !isTouch to isTouch - this allows native scrolling on touch devices while preserving drag prevention on mouse events
• The auto mode fix adds iteration counters and slide size validation to prevent infinite loops when slidesRect contains invalid values
• Issue itemsToScroll is broken when wrapAround is set to true #522 (itemsToScroll with wrapAround) was partially addressed but the main fix was reverted after test failures - this may need follow-up work
• Session URL: https://app.devin.ai/sessions/a6788ac4e74948408c54b566d3834873
• Requested by: @ismail9k