style: tint project list headers

[HonestMajority]

Summary

• tint the project list column header row light cyan while keeping the existing bold modifier
• leave labels, layout, counts, navigation, and data behavior unchanged

Validation

• cargo fmt -- --check
• cargo clippy --all-targets -- -D warnings
• cargo test
• git diff --check
• visual smoke: launched target/debug/agman in tmux and confirmed PROJECT/TASKS/AGENTS/DESCRIPTION rendered bold light cyan with unchanged alignment