feat(coding-agent): added /todo slash command actions in interactive-mode
- Added `/todo` slash command with edit, copy, start, done, drop, rm, append, and replace actions.
- Added InteractiveMode context/controller wiring to dispatch `/todo` commands through session runtime.
- Added todo controller parsing, editor-assisted edits, and commit syncing for session, UI, and storage updates.
- Changed todo persistence/restoration behavior, restored grep defaults, and removed chunk read mode and `pi-natives` references.