Remove Codex CLI version validation

[yvette-carlisle]

Summary

• remove Codex CLI version allowlist and the allow-unverified override
• reduce app-server preflight to capability/protocol checks and update probe output
• sync docs, Decodex App fallback arguments, and Decodex manual CLI skill guidance

Verification

• cargo check -p decodex --all-targets --all-features
• cargo make lint-fix
• cargo make fmt
• cargo make test
• cargo make test-decodex-app-stage
• cargo test -p decodex app_server --lib -- --nocapture
• cargo test -p decodex parses_serve -- --nocapture
• swift test --package-path apps/decodex-app
• semantic drift audit helper
• git diff --check
• residual keyword scans and decodex run/serve/probe help checks