tui: replace todo progress bar with inline pip-dot meter

Drop the heavy [████░░░░] block bar (and its dedicated line) in favor of
inline pip dots in the Todos header: ● done, ◐ active, ○ open. Small lists
render exactly 1:1 (no normalization) up to EXACT_PIP_FLOOR; larger lists
collapse proportionally to fit the panel width. Saves one vertical line per
todo widget and surfaces in-progress status.