TODO lists are now stored in .g3/sessions/<session_id>/todo.g3.md instead
of the workspace root. This prevents different g3 sessions from accidentally
picking up or overwriting each other's TODOs.
Changes:
- Add get_session_todo_path() function in paths.rs
- Update todo_read/todo_write handlers to use session-specific paths
- Remove TODO loading at Agent initialization (sessions start fresh)
- Update prompts to reflect session-scoped behavior
Fallback behavior preserved for planner mode (G3_TODO_PATH env var).
Dhanji R. Prasanna
64f27c0abc