Refresh README descriptions and audit resource links

[skratchdot]

Make the README's resource lists easier to browse with concise descriptions and sections grouped by purpose. Put project links before development instructions, link to the About/API/catalog docs, and separate articles, interactive visualizations, sorting with sound, visual galleries, source collections, and resources beyond sorting.

Correct moved URLs and misleading descriptions, merge duplicate destinations, replace stale VisualSort and Illustrated Algorithms demos with their source repositories, and remove a private video. Keep Casey Rule's Sounds of Sorting at its current address and both the sortvis gallery and source. Add Sort Algorithms, Princeton's sorting chapter, and CMU's comparison-sorting lower-bound lecture notes. Add author/project names to the README's spelling exceptions.

Validation:

• Audited the original 54 retained external URLs (HTTP 200) and verified all 6 local links exist.
• Inspected the five added destinations, including browser-rendered Casey Rule and Sort Algorithms pages and the sortvis gallery.
• Inspected destination content and YouTube metadata; third-party app features and video playback were not exhaustively tested.
• README and CSpell configuration formatting checks, README spelling checks, and git diff whitespace checks passed.

No application code changed; application tests were not rerun.