fix: smarter GPU detection to prefer Intel XPU over AMD iGPU

[Kosinkadink]

Problem

When a machine has an AMD CPU with integrated Radeon graphics (vendor 1002) and an Intel Arc discrete GPU (vendor 8086), the old pickGPU() priority (NVIDIA > AMD > Intel) incorrectly selects AMD — even though the AMD device is just an iGPU incapable of ROCm, and the user's actual compute GPU is the Intel Arc XPU.

Fixes #342

Changes

Core logic

• pickGPU() now accepts rich GpuDevice[] with name, VRAM, and discrete/integrated info
• New isAmdIgpu() heuristic classifies AMD GPUs using:
  • Device name patterns (e.g. "AMD Radeon(TM) Graphics" = iGPU, "RX 7900 XTX" = discrete)
  • Dedicated VRAM size (<512MB = iGPU, from Windows WMI)
  • Explicit discrete flag when available
• Priority is now: NVIDIA > discrete AMD > Intel (XPU) > AMD iGPU > CPU

Windows

• WMI query expanded to fetch Name + AdapterRAM per Win32_VideoController

Linux

• lspci parser extracts device descriptions for name-based iGPU heuristics
• sysfs reader simplified (vendor-only; lspci runs first with richer data)

Tests

• Comprehensive unit tests for isAmdIgpu and pickGPU covering:
  • The exact bug scenario (AMD iGPU + Intel Arc → picks Intel)
  • All single-GPU cases, all multi-GPU priority combinations
  • VRAM boundary conditions, explicit discrete flag, device order independence
• 533 tests passing, typecheck + lint + build all green