refactor: use simplified trace host contract

[Stephen Belanger (Qard)]

Summary

• Pin bt-daemon to the merged plugins PR #97 revision in Cargo.toml and Cargo.lock.
• Return HostRouteSelection from bt's trace host, containing only the auth selection and default project name.
• Let the daemon construct its own session route and trace-specific settings.

Validation

• cargo test --locked --bin bt (830 passed)
• pre-commit run --all-files --show-diff-on-failure (all hooks passed)

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Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-23T19:16:09.710476Z	77bb8ac	PR opened

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