[codex] Add backend mirror adapter

[WaffleBits]

Summary

• add a backend mirror adapter that normalizes vLLM/SGLang-style observations into release-gate inputs
• add runtime-lab mirror and runtime-lab mirror-gate CLI paths
• add adapter tests, a checked mirror fixture, generated report artifact, and docs

Why

Current high-compensation AI infrastructure postings are emphasizing production inference runtime integration, vLLM/SGLang-style serving, shadow/canary validation, and auditable rollback gates. This keeps the repo's existing deterministic release-policy shape while adding a concrete adapter surface for mirrored backend observations.

Validation

• WSL: cargo fmt --all --check
• WSL: cargo test --all-targets
• WSL: cargo clippy --all-targets --all-features -- -D warnings
• WSL: cargo run --release -- mirror-gate --input fixtures/backend_mirror_vllm_sglang.json --output artifacts/backend-mirror-report.json
• Windows: git diff --check

Note: native Windows cargo validation is blocked because this machine's MSVC Rust target cannot find link.exe; WSL validation passed.