ifcviewer: move initWgpu + probeAndCreatePool + shutdown into ViewportCore (#84-l)

The instance/adapter/device/queue/pool/surface-format wgpu lifecycle now
lives in ViewportCore — including the OOM-scoped pool size probe and
the worker-thread startup. ViewportWindow::initWgpu becomes a Qt shell
that handles env-var tuning + nav-button preset wiring, then delegates
to core_.initWgpu(); the VW-only pipeline builders (HiZ, edge, overlays,
pick) still run after. ViewportWindow::shutdown drops the VW-only
resources (depth, msaa, hiz, edge, overlays, pick) and lets
core_.shutdown() release the shared wgpu handles it now owns.

The wgpu-native log callback (wgpuSetLogCallback / WGPULogLevel) is
gated on !__EMSCRIPTEN__: it's not part of the W3C spec header, and
the emdawnwebgpu port doesn't ship wgpu.h — validation errors there
land in the browser console regardless.

Drive-by: update test_federation to compare HomeView::target as
Eigen::Vector3f (left stale by #79 when QVector3D was retired).

src/ifcviewer/ViewportCore.h

@@ -223,6 +223,33 @@ public:
     void ensureSelectionFlagsBuffer();
     void uploadSelectionFlagsIfDirty();
 
+    // ---- wgpu lifecycle ----------------------------------------------------
+    //
+    // initWgpu brings up the wgpu instance, gets the platform surface
+    // from host_->createSurface, requests adapter + device + queue,
+    // probes the streaming pool capacity, starts the background loader
+    // thread, and picks the swap-chain surface format. Does NOT build
+    // pipelines — the host runs the pipeline construction after this
+    // (so VW can still keep its HiZ / edge / pick / overlay builders
+    // co-located).
+    //
+    // `web_limits` forces the WebGPU spec mandatory floor (128 MB max
+    // storage binding, 256 MB max buffer) instead of the adapter's
+    // actual maximum — used by --web-limits to verify chunking fits
+    // through browser constraints.
+    //
+    // shutdown tears down everything ViewportCore owns. The host's own
+    // teardown (depth/MSAA/HiZ/edge/pick attachments + overlays) must
+    // run BEFORE this call so its device-owned resources release
+    // against a still-live device.
+    bool initWgpu(bool web_limits);
+    void shutdown();
+
+private:
+    bool probeAndCreatePool();
+
+public:
+
     // 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