Define the boundary the Path-A web-bring-up refactor will move things
across:
- ViewportHost.h is the embedder interface — surface creation,
framebuffer geometry, frame scheduling, quit, and notification
callbacks (onObjectPicked, onToolModeChanged, …). Desktop hosts
forward notifications to Q_SIGNALS; the future web host pushes
them to JS callbacks.
- ViewportCore.{h,cpp} is the platform-agnostic render-core target.
Empty today — the body fills in across the #78-#86 sequence as
each Qt subsystem (matrices, vectors, strings, timers, render
path, input) gets de-Qt'd and moved over.
- ViewportWindow now multiply-inherits ViewportHost alongside QWindow
and implements the host overrides as thin forwarders: createSurface
returns the cached surface_, requestFrame -> requestUpdate, quit ->
QCoreApplication::quit, onObjectPicked -> emit objectPicked.
Renamed the DPR accessor `dpr()` (vs `devicePixelRatio`) to avoid
the inherited-virtual clash with QWindow's qreal-returning version.
No method movement yet — this is purely the architectural scaffold so
subsequent commits have a destination.
Dion Moult