fix: centralize tmux lifecycle cleanup

[HonestMajority]

Summary

• centralize best-effort task tmux cleanup in archive, full delete, and permanent archived-task delete use cases
• make agent archive/permanent delete kill canonical tmux sessions best-effort from shared use-case logic
• remove duplicate CLI/TUI archive cleanup and cover lifecycle paths with real tmux integration tests

Validation

• cargo fmt -- --check
• cargo clippy --all-targets -- -D warnings
• cargo test
• git diff --check
• cargo test --test supervisor_tmux_test

Scope

• no broad legacy/orphan sweep
• no metadata-less tmux session discovery or deletion