Add live transcript attach and managed agent runs

[Stephen Belanger (Qard)]

Summary

• add import ... --attach for live Codex and Claude transcript following until Ctrl-C
• keep one translator and sink alive while an imported transcript grows, with incremental turn checkpoints and finalization
• add run <codex|claude> [ARGS...] using live plugin hook tracing rather than transcript-following
• inject Codex hooks through invocation-local config and Claude hooks through invocation-local settings, so tracing works without either plugin being installed or enabled
• preserve Codex hook security by using the normal one-time /hooks review instead of globally bypassing hook trust
• suppress inherited Braintrust plugin hooks for managed children while authorizing only the injected hook command, preventing duplicate spans
• preserve inherited stdio and the coding-agent exit status

Covers SDK-127 and SDK-128.

Validation

• cargo test --manifest-path bt-daemon/Cargo.toml --all-features --locked
• cargo clippy --manifest-path bt-daemon/Cargo.toml --all-targets --all-features --locked -- -D warnings
• make test
• generated live-hook settings accepted by the installed Codex and Claude CLIs
• standalone run help smoke test for both agent values