feat: harness bootstrap

[siisee11]

Summary

• install and vendor the harness-spec files into the repository
• scaffold the phase-1 docs, rules, plans, and reference structure
• add a Rust harnesscli with audit, validation, init, boot, observability, and cleanup surfaces
• wire Makefile and GitHub Actions harness CI

Verification

• make smoke
• make lint
• make typecheck
• make check
• make test
• make ci
• cargo test --manifest-path harness/Cargo.toml
• harness/target/release/harnesscli --output json audit .

Notes

• harnesscli boot start reports a structured sandbox bind failure in this environment instead of silently timing out.