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/FrameStats.h

@@ -38,6 +38,16 @@ struct FrameStats {
     std::uint32_t unique_meshes;
     std::uint32_t gl_draw_calls;        // wgpu draw-call count; name kept for bonsai parity
     std::uint32_t indirect_sub_draws;   // sub-draws packed into the chunk-indirect lists
+    // Chunk geometry pool occupancy (see BufferPool). wgpu exposes no
+    // adapter-wide VRAM query, so this is the viewer's own allocation,
+    // not the device total.
+    std::uint64_t vram_used_bytes;
+    std::uint64_t vram_capacity_bytes;
+    // Whole-device VRAM from the driver (NVML / sysfs, see GpuMemory.h).
+    // Desktop only; zero on web or when no backend could answer, so
+    // consumers must treat 0 as "unknown" rather than as empty.
+    std::uint64_t device_vram_used_bytes;
+    std::uint64_t device_vram_total_bytes;
 };
 
 #endif  // IFCVIEWER_FRAMESTATS_H