Includes the visualization steps for Shell Sort, following the same pattern as other sorts

[iamHarshithts]

Description

Demo

This PR adds Shell Sort visualization to the sorting algorithms category, following the same pattern as existing sorts.

What's Added

• Shell Sort algorithm with step-by-step visualization
• Gap-based comparison animations
• Consistent styling with other sorting algorithms
• Works with existing size and speed controls

Algorithm Details

• Time Complexity: O(n log n) to O(n²) depending on gap sequence
• Space Complexity: O(1) - in-place sorting
• Visualizes gap reduction and element comparisons at each step

Testing

Tested with various array sizes (5-100) and speed settings.

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