Remove DualTreeAtomicSwap; refresh docs

The BakedAspectGraph rendering mode supersedes DualTreeAtomicSwap for
GPU-driven animations. Delete DualTreeRenderer, the SetSpinYawSource
public API, the enum value, and all related state; the SpritePainter +
BakedAspectGraph pair covers everything DualTree did at lower cost.

Docs:
- README/usage/rendering-pipeline updated to reflect the current API
  surface (three sort algorithms now only mentioned in Highlights, not
  in the opening paragraphs).
- usage.md: replace the SetSpinYawSource walkthrough with a typed
  SetTransformAnimation walkthrough.
- Drop CombobulateSceneVisual from public docs; mark it as internal
  debugging/diagnostic in its xmldoc.

Author: arcadiogarcia

README.md

@@ -9,8 +9,10 @@ visual layer — no D3D, no SwapChainPanel, no shaders.
 > *([Wiktionary](https://en.wiktionary.org/wiki/combobulate))*
 
 Each quad becomes a `SpriteVisual` placed in 3D by a perspective
-`TransformMatrix`, with back-face culling and a topology-aware painter's
-algorithm to get the draw order right without a depth buffer.
+`TransformMatrix`. Back-face culling and a polygon sort keep the draw
+order right without a depth buffer, and a fully analytical *baked aspect
+graph* renderer can sustain GPU-driven animation with **zero CPU work
+per frame**.
 
 [composition]: https://learn.microsoft.com/windows/uwp/composition/visual-layer
 
@@ -38,27 +40,90 @@ samples/
 ## Getting Started
 
 1. Add the `Combobulate` NuGet package to your UWP or WinUI 3 app.
-2. Drop a `.obj` file into your app (e.g. `Assets/book.obj`, marked as
-   `Content` so it ships with the package).
-3. Place a `Combobulate` control in your XAML and point `Source` at the file:
+2. Place a `Combobulate` control in your XAML:
 
    ```xml
    <Page xmlns:c="using:Combobulate">
-       <c:Combobulate Source="ms-appx:///Assets/book.obj"
+       <c:Combobulate x:Name="Viewer"
+                      Source="ms-appx:///Assets/book.obj"
                       ModelScale="200"
                       RotationX="-30"
-                      RotationY="40" />
+                      RotationY="40"
+                      RotationZ="0" />
    </Page>
    ```
 
-That's it — no code-behind required. The control parses the `.obj` on demand,
-caches it process-wide, and auto-loads any `mtllib` referenced by the file
-(textures resolved relative to the `.obj`).
+   `Source` accepts an `ms-appx:///` URI, an absolute file path, or an
+   `ObjCache` key — geometry, materials (via sibling `mtllib`), and texture
+   surfaces are all loaded and cached process-wide.
 
-For everything else — loading from arbitrary paths or streams, supplying
-custom textures per face, live-updating pixels, the full property reference,
-the supported `.obj` / `.mtl` subset, and the caching model — see
-[**docs/usage.md**](docs/usage.md).
+3. Or parse an `.obj` yourself and assign the resulting model directly:
+
+   ```csharp
+   using Combobulate.Parsing;
+
+   var text = await FileIO.ReadTextAsync(
+       await StorageFile.GetFileFromPathAsync(@"C:\path\to\book.obj"));
+   var result = ObjParser.Parse(text);
+   Viewer.Model = result.Model;        // partial model on parse error
+   foreach (var err in result.Errors)  // optional: inspect parse diagnostics
+       System.Diagnostics.Debug.WriteLine(err);
+   ```
+
+That's it — the control rebuilds its visual tree whenever any of its
+inputs change.
+
+### Highlights
+
+- **Materials.** Auto-loaded from `mtllib` or supplied via `ObjMaterialPack`,
+  with live texture updates from `SoftwareBitmap` or streams.
+- **Three sort algorithms.** `Bsp` (default, exact, O(n)), `Newell`
+  (split-on-cycle, deformable-friendly), and `Topological` (legacy, fast).
+- **Composition-driven rotation.** `SetExternalRotation(ExpressionAnimation)`
+  binds rotation directly to the compositor; pair with `EnableAutoRefresh`
+  to keep cull and sort in lock-step with the compositor clock.
+- **Baked aspect graph.** Pre-computes every painter-order breakpoint
+  along an animation axis and emits one `ContainerVisual` per cell, each
+  gated by an opacity expression on a live scalar. Smooth GPU spin
+  without per-frame CPU cost. See
+  [docs/rendering-pipeline.md](docs/rendering-pipeline.md).
+
+For everything beyond "drop a control, point `Source` at a file" see the
+**[usage guide](docs/usage.md)** and the
+**[rendering pipeline](docs/rendering-pipeline.md)** doc.
+
+### Supported `.obj` subset
+
+- `v x y z [w]` — vertex positions
+- `vt u v [w]` — texture coordinates
+- `vn x y z` — vertex normals (parsed; not used for shading today)
+- `f a b c d` — **quad** faces; `a/ta/na` style references accepted
+- `usemtl <name>`, `mtllib <file>` — material binding and library load
+- `o`, `g`, `s` — preserved; `l`, `p`, `vp`, curves/surfaces are ignored
+
+Faces must be **quads** (triangles and n-gons are reported as parse errors).
+Wind each face so that `(V1 - V0) × (V3 - V0)` points outward — that's the
+direction the renderer treats as front-facing for back-face culling.
+
+See [`samples/book.obj`](samples/book.obj) for a worked example.
+
+### Control properties at a glance
+
+| Property | Type | Default | Notes |
+| --- | --- | --- | --- |
+| `Source` | `string?` | `null` | Path, `ms-appx:///` URI, or `ObjCache` key |
+| `Model` | `ObjModel?` | `null` | Direct model assignment |
+| `Materials` | `ObjMaterialPack?` | `null` | Overrides any auto-loaded `mtllib` |
+| `MaterialMode` | `MaterialMode` | `Auto` | `Auto` / `UseDiffuse` / `UseFallback` |
+| `ModelScale` | `double` | `100` | Pixels per model unit |
+| `EnablePerspective` | `bool` | `true` | Apply perspective `M34` to the root |
+| `PerspectiveDistance` | `double` | `0` | Focal distance in px (0 = host width) |
+| `RotationX/Y/Z` | `double` | `0` | Euler angles in degrees |
+| `SortAlgorithm` | `SortAlgorithm` | `Bsp` | `Bsp` / `Newell` / `Topological` |
+| `CullMarginDegrees` | `double` | `0` | Widen back-face cull cone for GPU lag |
+| `RenderingMode` | `RenderingMode` | `SpritePainter` | `SpritePainter` / `BakedAspectGraph` |
+
+Full descriptions and examples are in the [usage guide](docs/usage.md).
 
 ## Releasing