openup: architecture notebook + EA diagram renders

- analysis-design/architecture-notebook.md: Architecture Notebook work
  product in the keyfob docx template structure (10 sections), grounded
  in mapping / design note / supplementary specs; embeds the component
  model and all 12 realization figures
- scripts/openup/export-diagram-images.ps1: read-only EA COM renderer
  (EA-15 findings: image API on ProjectInterface, OpenDiagram before
  export or blank stub, type 0 = PNG); renders reflect manual layouts
- renders: requirements/use-case-overview.png, analysis-design/
  uc-01..12-realization.png + component-architecture.png; embedded as
  figures in use-case-model.md and uc-realization-mapping.md
- BUILD-CHECKLIST 6.4 documents the exporter

docs/openup/requirements/use-case-model.md

@@ -28,6 +28,10 @@ Scope: the **existing implemented system** (server MVP as of `wi-2-architecture-
 | UC-11 | Study Magic | Player | — |
 | UC-12 | Level Up at Review Board | Player | — |
 
+![Skara Brae Use Case Overview](use-case-overview.png)
+
+*Figure 1: Use case overview (rendered from the EA model, `docs/openup/model/skara-brae.eapx`, via `scripts/openup/export-diagram-images.ps1`).*
+
 Shared sub-flow **Regenerate Resources**: the system recomputes time-based regeneration **at specific call sites only** — list characters, view character, run adventure, and train stat (routes/mod.rs:264–266, 331, 442, 642). Energy +1 per 180 s, nerve +1 per 300 s, HP +5% of max per 300 s (only if alive and injured), capped at maxima; `last_regen` advances to now. It is **not** applied by equip/unequip, gym view, shop, heal, songs, spells, or level-up.
 
 ---