#2725 bench: RX 7900 XT (Windows HIP) community results + fix BENCH.bat on GBK Windows

Description

Two commits:

1. `tools/strata_bench.py`: `project_version()` called `CMakeLists.txt.read_text()` without an encoding. On a Chinese Windows install (GBK default) decoding raises `UnicodeDecodeError` — and because that is a ValueError it slips past the `except OSError` and kills the whole benchmark before the first test. Pinning `encoding="utf-8"` fixes it; reproduced on the current main, and the full suite runs afterwards.

2. `bench/results/2026-10-16-community-rx-7900-xt-swift-1-5-iq3-xxs`: community benchmark row for a Windows HIP setup on an RX 7900 XT (24 GB), Swift-Qwen3.8-Flash-Next GSQ-RCO IQ3_XXS, engine 0.1.44.1, 320K context (yarn 1.25), int8 KV, spec 4 + MTP, vision through a Vulkan encoder pinned to the AMD card. Medians: chat decode 50.7 tok/s (TTFT 0.65 s), 4K prompt 416 tok/s, 16K prompt 560 tok/s, agent session cache hit 68.4%, agent decode 53.6 tok/s.

One note on the sanitizer: `results.json` still contained a second data folder (`D:\...` style paths outside the Strata folder and the user home) that the scrubber missed; I cleaned it by hand in this branch. Worth widening the scrubber if you ever get reports from multi-drive installs.