bonsaiviewer: show pool and device VRAM in the performance stats

FrameStats gains the geometry pool's used/capacity bytes and, on desktop,
the device-wide used/total reported by the driver (NVML via dlopen, or
amdgpu/i915 sysfs, matched to the wgpu adapter's vendor/device id so a
switchable-graphics laptop reports the card wgpu actually picked). The
device query is polled once a second, not per frame. Web has no VRAM
query, so the device figure is omitted there.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/ifcviewer/GpuMemory.h

@@ -0,0 +1,62 @@
+/********************************************************************************
+ *                                                                              *
+ * This file is part of IfcOpenShell.                                           *
+ *                                                                              *
+ * IfcOpenShell is free software: you can redistribute it and/or modify         *
+ * it under the terms of the Lesser GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3.0 of the License, or          *
+ * (at your option) any later version.                                          *
+ *                                                                              *
+ * IfcOpenShell is distributed in the hope that it will be useful,              *
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of               *
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                 *
+ * Lesser GNU General Public License for more details.                          *
+ *                                                                              *
+ * You should have received a copy of the Lesser GNU General Public License     *
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.         *
+ *                                                                              *
+ ********************************************************************************/
+
+
+#ifndef GPUMEMORY_H
+#define GPUMEMORY_H
+
+#include <cstdint>
+
+// How much video memory the card has, and how much of it is in use.
+//
+// WebGPU deliberately exposes neither -- `maxBufferSize` reports 1 TB on this
+// stack and is useless as a proxy -- so this goes outside the graphics API.
+// That is legitimate on desktop, where the viewer is a native app, and it is
+// the number every other part of the residency story needs: a gauge to show
+// the user, a budget to keep the pool under, and a pre-flight check that can
+// refuse a model before it wedges the session.
+//
+// Matching the right GPU matters. On a laptop with switchable graphics the
+// obvious sysfs entry is often the *integrated* chip rather than the one wgpu
+// selected -- measured here: /sys/class/drm/card1 reports a 512 MB AMD iGPU
+// while wgpu is running on a 4 GB GeForce. So the query takes the vendor and
+// device ids from WGPUAdapterInfo and matches on them.
+namespace ifcviewer {
+
+struct GpuMemoryInfo {
+    std::uint64_t total_bytes = 0;
+    std::uint64_t used_bytes  = 0;
+    // False when no backend could answer -- an unknown driver, a platform
+    // without a query, or a device the probe could not match. Callers must
+    // treat that as "unknown" and not as "zero": refusing to load because an
+    // unavailable query returned 0 would be worse than not asking.
+    bool          valid       = false;
+
+    std::uint64_t free_bytes() const {
+        return total_bytes > used_bytes ? total_bytes - used_bytes : 0;
+    }
+};
+
+// Query the GPU wgpu selected. `vendor_id` / `device_id` come from
+// wgpuAdapterGetInfo. Cheap enough to call once a second; not per frame.
+GpuMemoryInfo queryGpuMemory(std::uint32_t vendor_id, std::uint32_t device_id);
+
+}  // namespace ifcviewer
+
+#endif