chore(pr47): drop mission perf docs from PR scope + default AUTO_DETECT_BACKENDS=OFF

The docs/perf/*.md files documented the e2e optimization mission and are
not part of the Ascend operator kernel scope this PR delivers. Removed
from the tip; unchanged in intermediate history.

AUTO_DETECT_BACKENDS default flipped to OFF in pyproject.toml to avoid the
openblas link failure in the ascend CI container (master's torch-backend
auto-detect requires libgfortran symbols not present there). Build still
enables torch backend explicitly when requested.

Author: zhangyue