Decide the canonical runtime image root (ADR-0014)

assets/images/ is now the runtime root for composed interface/scene art:
ui/ for screen and panel art, scenes/ for full-frame scene art. Tiled PBR
textures remain under assets/textures/; docs/screens/designs and concepts stay
reference-only; QA captures stay under docs/screenshots. Mockups that become
runtime art are copied/processed with a new name (no overwrites) and always
have a code fallback.

Records the convention in MEMORY, adds ADR-0014 to the architecture index, and
closes the first storage-restructure TODO item.

docs/architecture.md

@@ -167,6 +167,7 @@ Architecture decisions are recorded as ADRs:
 - [ADR-0011: Aim-free selection and precision walk](adr/0011-aim-free-selection-and-precision-walk.md)
 - [ADR-0012: Surface materials and generated props](adr/0012-surface-materials-and-generated-props.md)
 - [ADR-0013: Blender-authored NPC characters and baked materials](adr/0013-blender-authored-npc-characters.md)
+- [ADR-0014: Canonical runtime image root and image conventions](adr/0014-runtime-image-root.md)
 
 ## 10. Quality Requirements