Phase 4.3: Grid auto-creates GridView with rendering property sync

Grid.__init__() now auto-creates a GridView that shares the Grid's
data via aliasing shared_ptr. This enables the Grid/GridView split:

- PyUIGridObject gains a `view` member (shared_ptr<UIGridView>)
- Grid.view property exposes the auto-created GridView (read-only)
- Rendering property setters (center_x/y, zoom, camera_rotation, x, y,
  w, h) sync changes to the view automatically
- Grid still works as UIDrawable in scenes (no substitution) — backward
  compatible with all existing code and subclasses
- GridView.grid returns the original Grid with identity preservation
- Explicit GridViews (created by user) are independent of Grid's own
  rendering properties

Addresses #252. All 260 tests pass, no breaking changes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/UIBase.h

@@ -27,9 +27,11 @@ typedef struct {
 } PyUICaptionObject;
 
 class UIGrid;
+class UIGridView;
 typedef struct {
     PyObject_HEAD
     std::shared_ptr<UIGrid> data;
+    std::shared_ptr<UIGridView> view;  // #252: auto-created rendering view (shim)
     PyObject* weakreflist;  // Weak reference support
 } PyUIGridObject;