[codex] add session dashboard tui

[jiunbae]

Summary

• add the muxa dashboard session-card TUI for operating panes and PTY sessions without attaching
• reuse stats ACT/WACT attribution in the dashboard and document the new CLI flow
• add target cycling, inspector/capture panels, zellij action guards, and render/unit coverage

Validation

• cargo fmt --all -- --check
• cargo clippy -p muxa-cli --all-targets -- -D warnings
• cargo test --workspace
• pre-push hook: cargo fmt --all -- --check, cargo clippy --workspace --all-targets -- -D warnings