ifcviewer: move wgpu lifecycle state ownership into ViewportCore

First chunk of the #84 ViewportCore extraction. The seven wgpu lifecycle
handles (instance, adapter, device, queue, surface, surface_format,
surface_configured) now live as ViewportCore members; ViewportWindow
keeps reference aliases pointing at ViewportCore's storage so its
existing render-method bodies don't need a `core_.` prefix added at
every call site — 230+ touches deferred until each method moves
across.

Member init order in ViewportWindow's constructor:
  core_(this)               → constructs ViewportCore with host_=this
  instance_(core_.instance_) → binds the alias to core_'s field
  …                           same for adapter/device/queue/surface/…

Friend declaration on ViewportCore::ViewportWindow lets the references
bind to its private fields. The friend bond shrinks each commit as
render methods (and their `device_` / `queue_` references) migrate into
ViewportCore proper; the goal state is no friend and no aliases.

Next #84 chunks (separate commits) move pipelines, models_gpu_, pool_,
streaming_thread_, then the render/cull/encode methods. Each leaves
the desktop build green.

Builds: desktop / bonsai / web all green. Tests 100/100.

src/ifcviewer/ViewportCore.h

@@ -20,17 +20,20 @@
 #ifndef VIEWPORTCORE_H
 #define VIEWPORTCORE_H
 
-// Platform-agnostic render core. Owns the wgpu state + scene state +
-// per-frame render path. Talks to its embedder through ViewportHost
-// (window/canvas surface, scheduling, notifications) — has no Qt or
-// browser dependencies of its own.
+// Platform-agnostic render core. Owns the wgpu lifecycle state +
+// (eventually) scene state + per-frame render path. Talks to its
+// embedder through ViewportHost (window/canvas surface, scheduling,
+// notifications) — has no Qt or browser dependencies of its own.
 //
-// Empty for now: this header / TU is the placeholder for the
-// incremental Path-A refactor (#77-#86). Each subsequent commit moves
-// one subsystem out of ViewportWindow.cpp into here and updates the
-// public surface accordingly. Until that work lands, ViewportWindow
-// retains its render body; this class is just the target for the
-// move.
+// First migration target (#84-a): wgpu instance/adapter/device/queue/
+// surface ownership. The next subsystems (pipelines, models, render
+// path) move incrementally across subsequent commits — each leaving
+// the desktop build green. ViewportWindow currently holds reference
+// members pointing back at ViewportCore's storage so its body doesn't
+// have to acquire a `core_.` prefix on every wgpu touch. Those
+// references shrink as render methods themselves move over.
+
+#include <webgpu/webgpu.h>
 
 #include "ViewportHost.h"
 
@@ -44,8 +47,28 @@ public:
 
     ViewportHost* host() const { return host_; }
 
+    // Friend access for ViewportWindow's reference proxies. As each
+    // render method moves into ViewportCore it stops needing these
+    // (it touches the fields directly); once everything has migrated
+    // the friend declaration goes away.
+    friend class ViewportWindow;
+
 private:
     ViewportHost* host_;
+
+    // ---- wgpu lifecycle state ------------------------------------------------
+    //
+    // Plain pointers (wgpu C handles); zero-init means "not yet
+    // initialised". Owned by ViewportCore now; reference members in
+    // ViewportWindow alias these so the existing call sites don't
+    // need to change to use a `core_.` prefix.
+    WGPUInstance      instance_           = nullptr;
+    WGPUAdapter       adapter_            = nullptr;
+    WGPUDevice        device_             = nullptr;
+    WGPUQueue         queue_              = nullptr;
+    WGPUSurface       surface_            = nullptr;
+    WGPUTextureFormat surface_format_     = WGPUTextureFormat_Undefined;
+    bool              surface_configured_ = false;
 };
 
 #endif  // VIEWPORTCORE_H

src/ifcviewer/ViewportWindow.cpp

@@ -606,7 +606,19 @@ static WGPUStringView svFromCStr(const char* s) {
 // -----------------------------------------------------------------------------
 
 ViewportWindow::ViewportWindow(QWindow* parent)
-    : QWindow(parent) {
+    : QWindow(parent),
+      core_(this),
+      // Bind reference aliases to ViewportCore's storage so the
+      // existing `device_` / `queue_` / … sites in this TU keep
+      // working unchanged. Each reference goes away as its owning
+      // render method moves into ViewportCore.
+      instance_          (core_.instance_),
+      adapter_           (core_.adapter_),
+      device_            (core_.device_),
+      queue_             (core_.queue_),
+      surface_           (core_.surface_),
+      surface_format_    (core_.surface_format_),
+      surface_configured_(core_.surface_configured_) {
     // wgpu doesn't need a GL context; we just need a real native window
     // whose backing layer matches the GPU API wgpu will drive.
     //

src/ifcviewer/ViewportWindow.h

@@ -634,16 +634,25 @@ private:
     void recomposeAndUploadModel(uint32_t model_id);
 
     bool wgpu_initialized_ = false;
-    bool surface_configured_ = false;
     int  configured_w_ = 0;
     int  configured_h_ = 0;
 
-    WGPUInstance      instance_       = nullptr;
-    WGPUAdapter       adapter_        = nullptr;
-    WGPUDevice        device_         = nullptr;
-    WGPUQueue         queue_          = nullptr;
-    WGPUSurface       surface_        = nullptr;
-    WGPUTextureFormat surface_format_ = WGPUTextureFormat_Undefined;
+    // ---- wgpu lifecycle state aliases ----------------------------------
+    //
+    // Actual storage lives in core_ (declared below; ViewportWindow is a
+    // friend of ViewportCore so these references can bind). Existing
+    // member-access sites in ViewportWindow.cpp keep working unchanged —
+    // they just resolve to core_.device_ etc. through these references.
+    // Each one is removed when its owning render method moves into
+    // ViewportCore (#84-b onwards).
+    ViewportCore core_;
+    WGPUInstance&      instance_;
+    WGPUAdapter&       adapter_;
+    WGPUDevice&        device_;
+    WGPUQueue&         queue_;
+    WGPUSurface&       surface_;
+    WGPUTextureFormat& surface_format_;
+    bool&              surface_configured_;
 
     // Render pipeline + bind group layouts (built once after init).
     WGPUShaderModule       main_shader_module_ = nullptr;