Replace estimated values with clpeak measurements: DRAM 216-233 GB/s,
GPU clocks confirmed 2900 MHz under load (ROCm #5750 is sysfs reporting
only). Correct backend recommendation to Vulkan RADV (2.7x faster tg
than ROCm at 131K). Update KV cache recommendation to q4_0. Add
Nemotron-Cascade-2 to coder shootout results. Remove Nemotron-3-Nano
from catalog (replaced by Cascade-2). Update Q4_K_L to Q4_K_XL entry.
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