Build out all 27 modules + capstone (#1)

Co-authored-by: claude <claude@jpaul.io>
Co-committed-by: claude <claude@jpaul.io>

modules/21-skills-teaching-the-ai-your-playbook/lab/tasks-app/CHANGELOG.md

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+# Changelog
+
+Newest entries on top. One line per user-visible change.
+
+## Unreleased
+
+- Add `count` command: print how many tasks are still pending.
+- Add `done <index>` command: mark a task complete.
+- Initial CLI: `add` and `list`.