[codex] refactor(config): extract harness posture module

[Hmbown]

Summary

• Moves the harness posture/profile data model out of crates/config/src/lib.rs into a focused crates/config/src/harness.rs module.
• Moves the built-in harness profile seeds and profile matching helpers with the type they support, keeping the boundary cohesive.
• Re-exports the harness types and built_in_harness_profiles from the crate root so existing callers keep the same public API.

Refs #3311

Testing

• cargo fmt --all -- --check
• cargo clippy -p codewhale-config --all-targets --locked
• cargo test -p codewhale-config --locked harness
• cargo test -p codewhale-config --locked config
• cargo test -p codewhale-config --locked
• git diff --check
• cargo clippy --workspace --all-targets --all-features
• cargo test --workspace --all-features

Checklist

• Updated docs or comments as needed (moved existing rustdoc with the types)
• Added or updated tests where relevant (existing harness/config coverage preserved)
• Verified TUI behavior manually if UI changes (N/A, config crate extraction only)
• Harvested/co-authored credit uses a GitHub numeric noreply address (N/A, no harvested code)