Milestone 3: Interface and Report

Build summarize(tasks) -> dict with keys total (all) and open (done == 0); and main(argv, repo) dispatching: ['add', title] → service add via repo, print 'added', return 0; ['list'] → print each open task's title in order, return 0; anything else → error to stderr, return 2. Both functions annotated (main returns int).

Difficulty: advanced