The dtparam=pciex1_gen=3 was being appended after the [all] section,
but RPi firmware requires PCIe dtparams in the [pi5] section.
Switch from configTxtAppend to full configTxt replacement to control
section ordering. Also add dtparam=pciex1 to explicitly enable the
external PCIe link.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Adds dtparam=pciex1_gen=3 to config.txt overlay. Benchmarked Gen 2 baseline
on all 3 pg nodes showing consistent ~375 MB/s write throughput, bottlenecked
by the Gen 2 x1 lane limit.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>