Fix DGX Spark hardware metadata

[EHxuban11]

• Report unavailable GPU capacity as null and GB10 memory as OS-visible shared CPU/GPU memory.
• Detect Arm CPU names when /proc/cpuinfo has no x86-style model name; preserve dedicated GPU reporting.
• Supports DavidDiazMerino's Spark contribution: Add YOLOv9-T and RF-DETR-S benchmarks on DGX Spark vision-analysis#14.
• Verified: 83 tests passed; Ruff checks passed.
• Not verified: detection on a physical DGX Spark. Hardware probes were tested with fixtures.

Code provenance

• Original changes to first-party code; no third-party code copied or adapted.