doc: MUI framework documentation — whitepaper overview, SDK-derived architecture, layout mockups

- README.md: comprehensive whitepaper-style overview with historical context,
  paradigm shift analysis, BOOPSI comparison, version history (Stefan Stuntz
  as sole author 1.0-3.8), licensing model breakdown, parallel evolution
  timeline (NeXTSTEP/Qt/MUI convergence), community-sourced developer values
- 02-architecture.md: complete rewrite from MUI 3.8 SDK sources — object
  lifecycle state machine, three-level resource binding, method dispatch chain,
  notification system with sequence diagrams, layout engine internals
  (3-pass constraint system), input handling, dynamic object linking,
  rendering model, tag ID namespace
- 05-layout-system.md: Mermaid visual mockups for VGroup, HGroup, nested
  groups, column grids, scrollgroups, file requester real-world example,
  layout algorithm and resize sequence diagrams
- frameworks/README.md: framework index with comparison table
- All content in American English

09_intuition/frameworks/README.md

@@ -0,0 +1,24 @@
+[← Home](../../README.md) · [Intuition](../README.md)
+
+# GUI Frameworks
+
+AmigaOS spawned several GUI frameworks beyond the built-in GadTools/BOOPSI system. These frameworks provide layout management, user customization, and richer widget sets — features that the base Intuition API does not offer.
+
+## Framework Index
+
+| File | Framework | Era | Description |
+|---|---|---|---|
+| [mui/](mui/) | **MUI** (Magic User Interface) | 1993– | De-facto standard. Architecture, developer guide, code examples |
+| *reaction.md* | **ReAction** / ClassAct | 1997– | Hyperion's official OS 3.5+ GUI toolkit |
+| *bgui.md* | **BGUI** | 1994– | Lightweight BOOPSI-based layout system |
+
+## Comparison
+
+| Feature | MUI | ReAction | BGUI | GadTools |
+|---|---|---|---|---|
+| Layout engine | ✅ Constraint-based | ✅ Constraint-based | ✅ Basic | ❌ Manual |
+| User preferences | ✅ Full | ⚠ Limited | ❌ None | ❌ None |
+| Custom classes | ✅ MCC ecosystem | ✅ MakeClass | ✅ MakeClass | ❌ N/A |
+| Availability | Aminet (free runtime) | OS 3.5+ bundled | Aminet (free) | ROM built-in |
+| Platforms | AmigaOS, MorphOS, AROS | AmigaOS 3.5+ only | AmigaOS 2.0+ | AmigaOS 2.0+ |
+| Adoption | Very high | Moderate | Low | Universal |