feat: add counting sort with unified bucket/output visualizer

[gian-gg]

Description

Adds a complete Counting Sort implementation and visualization flow, including stable output construction using cumulative counts.

Summary of changes:

• Added counting-sort to the algorithm registry and marked it as implemented.
• Added route wiring for /algorithms/counting-sort.
• Implemented CountingSortPage with:
  • counting/frequency phase
  • cumulative bucket phase
  • stable placement phase (right-to-left input traversal)
• Extended sorting frame types to support multi-layer visualization data:
  • input array
  • buckets
  • output array
• Upgraded SortingVisualizer to support 3 stacked levels when bucket/output data is present.
• Added bucket range display in section title (e.g. Buckets (10 to 100)).
• Added bucket tooltip details with visible index/value/count on hover.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have checked that my commit message follows conventional commits

Preview

counting-sort-preview.mov