docs: prepare runtime for public review

[rustfuture]

Summary

• add CI scheduling headroom to the positive provider test without weakening timeout tests
• replace the stale top-level evaluation summary with the current independent results
• add changelog, contribution, and security guidance
• remove machine-specific absolute paths from tracked evidence
• align the package with v0.1.1

Verification

• cargo fmt --check
• cargo check --locked --all-targets
• cargo clippy --locked --all-targets -- -D warnings
• cargo test --locked (47 passed)
• positive provider test repeated 10/10
• full-history and working-tree gitleaks scans: 0 findings