Viewport capped at ~105–125 fps; render thread stuck in Windows graphics kernel calls

Painter 12.2.0 (build 5909), Vulkan | Windows 11 build 26300
RTX 4070 SUPER 12 GB, driver 617.42| Ryzen 7 9800X3D, 32 GB | 4K 240 Hz

Issue:
The viewport runs at ~100–110 fps when orbiting (peaks ~125), ~120 fps in an empty scene. Same at 4K and 1440p. The GPU is mostly idle.

Findings:
- PresentMon: ~9 ms per frame, but GPU busy only ~4 ms
- Nsight Systems: "SAL Render Thread" is ~79% busy. ~80% of that time is in dxgkrnl.sys / dxgmms2.sys, called from nvoglv64.dll. Painter's own code is ~10%.

No change with: resolution, Viewport Scaling, Windows scaling, refresh rate, G-Sync, NVIDIA present method (native/DXGI), Threaded Optimization off, HAGS on/off, another NVIDIA driver, --vram-budget 8000, SVT hardware acceleration off, viewport effects off, overlays (RTSS/OBS) disabled.

Expected: fps limited by the GPU, not by per-frame driver/kernel overhead.