Describe level-2 milestones/themes, level-3 workstreams and the rule that
completed workstreams stay under their parent until the whole milestone is
done. Add a milestone-shaped recommended format and align the changelog/tag
steps with nested sections.
- AGENTS.md now requires agents to mark a task [-] while claimed/in progress and
only use [x] after implementation and verification, with an example
- copied the 21 reference mockups from docs/screens/designs/ into the runtime
root assets/images/ui/ (byte-identical names); docs/screens/designs/ stays as
the reference-only copy per ADR-0014
- MEMORY records where the copies live and that screen_designs.py still reads
the docs tree until the code-path migration
First storage-restructure TODO item completed.