Render About and API pages from Markdown docs

[skratchdot]

The About and Algorithm API pages previously embedded their content in TSX. Render them from docs/about.md and docs/api.md through a shared Markdown component, so content can be edited directly and additional documents can be published with small static routes.

The renderer supports tables, code blocks, and links between published documents under the site's base path. Both pages match the header width; the API retains bold methods and adds labeled marker-color swatches. About tells the 2013 origins and 2026 AI modernization story, while the API explains recording and item references with a runnable insertion-sort example. The header now links to GitHub through an accessible black Octocat icon.

Development documentation explains how to publish more pages without exposing every file in docs/.

Validation:

• pnpm run check: lint, formatting, spelling, types, 362 unit tests, and static production build passed.
• Production browser suite: 38 tests passed, including responsive header layout and Markdown navigation without JavaScript.
• API example verified with empty, single-item, reversed, duplicate, and sorted inputs.