move docs to docs/ folder, merge architecture files, update references

docs/DESKTOP-DESIGNER.md

@@ -0,0 +1,40 @@
+# Desktop Designer
+
+The desktop designer (`designer/`) provides rapid UI development with:
+
+- **Hot-reload**: Automatically reloads when RML/RCSS/Lua files change
+- **UI Hierarchy Dumping**: Exports element tree to JSON for inspection
+- **Screenshot Capture**: PNG export via F12 key
+- **Logging**: Detailed output for debugging navigation and events
+- **Action Recording**: Record mouse/keyboard interactions to JSON
+- **Action Playback**: Replay recorded interactions with timing
+
+## Key Files
+
+| File | Purpose |
+|------|---------|
+| `designer/src/main.cpp` | Main entry point, GLFW window, event loop |
+| `designer/src/desktop_kernel.cpp` | RmlUi context management, rendering |
+| `designer/src/testing/ui_inspector.cpp` | UI hierarchy JSON export |
+| `designer/src/testing/visual_capture.cpp` | PNG screenshot capture and comparison |
+| `designer/src/testing/action_recorder.cpp` | Record user interactions to JSON |
+| `designer/src/testing/action_player.cpp` | Playback recorded actions |
+| `designer/src/backend/RmlUi_Backend_GLFW_GL3.cpp` | GLFW backend with input hooks |
+
+## Command Line Options
+
+```
+--log <path>        Write logs to file
+--hierarchy <path>  Dump UI hierarchy JSON each frame
+--dump              Single-shot dump mode (screenshot + hierarchy)
+--record <path>     Enable recording mode (F5 to start/stop)
+--playback <path>   Play back recorded actions from JSON
+```
+
+## Keyboard Controls
+
+| Key | Function |
+|-----|----------|
+| F5 | Start/stop recording (when --record is enabled) |
+| F6 | Pause/resume playback (when --playback is enabled) |
+| F12 | Take screenshot |