Remove generated audit artifacts and redundant root documentation

[mxsm]

Context

The repository currently ships a generated architecture/performance audit HTML file and four root-level topic documents that duplicate the README, executable tests, and GitHub Actions contracts. These artifacts increase package size, create multiple sources of truth, and are not required by the public crate API.

Objective

Keep the repository documentation surface focused on the README and changelog while preserving executable evidence in tests, scripts, and workflows.

Scope

• remove the generated architecture/performance audit HTML file
• remove API.md, LAYOUT.md, PERFORMANCE.md, and SAFETY.md
• replace README links to removed files with direct references to tests, scripts, source, or workflows
• add a repository contract that prevents the generated audit artifacts from being shipped again
• leave the untracked docs/ directory untouched

Acceptance criteria

• no tracked generated audit report remains
• README and packaged documentation contain no broken references to removed files
• README.md and CHANGELOG.md remain the root documentation entry points
• Rust, repository-contract, rustdoc, and package verification pass
• the release package excludes the removed artifacts and all docs/** content