#750 docs: describe a targeted ROCr USERPTR reclaim workaround

描述

## Summary

Document a targeted Linux/ROCr 7.2 workaround for verification stalls correlated with host-memory reclaim and KFD USERPTR eviction/restoration. Link the runtime's allocation path and exact environment-variable handling, show how to compare and revert the setting, and describe resource constraints.

The evidence is summarized without host identifiers, private logs or request content. Five paired synthetic runs had similar median seven-request completion times and fewer observed long stalls with the alternative allocation path, while solo/first-output timings were slightly worse. The document explicitly avoids a universal speed or reliability claim, leaves defaults unchanged, and does not recommend the setting for untested runtimes or Windows.

## Validation

Checked the ROCr 7.2 source cited in the document, JSON snippet syntax, and `git diff --check`. This is documentation only; no setup defaults or runtime code change.