Classify saved sessions by live work rather than pane existence

Operator status previously treated any tmux pane in a workspace as equivalent to active work. The new classifier uses tmux pane command/path metadata as a soft signal, treats plain shells as idle, and adds dirty-worktree abandoned markers to status and session-list output for clawhip consumers.

Constraint: Keep issue ultraworkers#320 prototype minimal and additive without new dependencies

Rejected: Screen-scraping pane output | fragile and broader than needed for lifecycle classification

Confidence: high

Scope-risk: narrow

Tested: cargo test -p rusty-claude-cli

Tested: cargo check -p rusty-claude-cli

Not-tested: cargo clippy -p rusty-claude-cli --all-targets -- -D warnings is blocked by pre-existing commands crate clippy::unnecessary_wraps warnings

Author: Yeachan-Heo