Build one planned slice

1. Read PLAN.md and select the first unchecked task in build order. If no unchecked task remains, report that and stop.
2. Implement only that task end to end, including data, API, and UI as needed. Use the frontend-design skill for UI work.
3. Run the app and the relevant checks, fix errors caused by the change, and confirm the task works.
4. Mark that task complete in PLAN.md and commit the change with a clear message. Do not start another task.
5. Report in exactly two lines what works and what was committed.