Claim TODO tasks with [-]; promote mockups to assets/images/ui

- 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.

AGENTS.md

@@ -39,6 +39,10 @@ All planned implementation work must be represented in `TODO.md`.
 - Use checkbox items for each concrete task.
 - Keep tasks small enough to complete and review independently.
 - Add new tasks when discoveries expand the scope.
+- When starting a task, claim it for the agent workflow by changing `[ ]` to `[-]`. Keep it `[-]`
+  while implementation or verification is in progress; only change it to `[x]` after the work and
+  relevant checks are finished. If work is abandoned or blocked, leave a clear note and return the
+  item to `[ ]` (or add a follow-up task).
 - Mark a task complete only after the implementation and relevant verification are finished.
 - If any verification check fails, do not mark the task complete. Fix the failure, or if it cannot be fixed, add a follow-up task to `TODO.md`, record the failure in `MEMORY.md`, and report it in the handoff summary.
 - Do not use prose status updates as a substitute for checkboxes.
@@ -52,7 +56,7 @@ Recommended format:
 ## Core Gameplay
 
 - [ ] Add player movement controls.
-- [ ] Implement NPC approach behavior.
+- [-] Implement NPC approach behavior. (claimed; implementation/verification in progress)
 - [x] Define escalation levels.
 
 ## Documentation