Repository root carries unreferenced build artifacts and a stale spec file #57

Found while reviewing project structure for #56.

The repository root holds files that nothing references:

• sudoku7-dark.png, sudoku7-interactive.png, sudoku7-light-clean.png, sudoku7-light.png, sudoku7-pencil.png, sudoku7-test.png: 240 KB of development screenshots
• snake.md: 20 KB feature spec for the /snake route

rg finds no reference to the screenshots anywhere in the repository. snake.md is referenced by nothing; the /snake route lives in src/pages/snake.tsx and docusaurus.config.ts.

Acceptance criteria

• The six sudoku7-*.png files are either deleted or moved under static/ and referenced from the page that needs them.
• snake.md is either deleted or moved to a documentation location where it is reachable.
• The built site is unchanged for anything that used these files.