Documents the new installer: A/B slot install with no repartitioning,
factory archives to /data, signature-verified forgefirm.fw, ffboot
switching, offline install, and the automatic legacy-layout
migration.
install-forgefirm.sh completed silently broken when the download, flash
write, mount or uEnv rewrite failed - add die() checks around every
critical step (audit N13/M12) and download the release asset under the
exact Scarthgap artifact name (forgefirm-image-glowforge.rootfs.wic.gz)
so uploads need no renaming. ffboot no longer depends on the never-
provisioned /etc/fw_env_mmcblk2.config: it falls back to
/etc/fw_env.config (which both the factory and ForgeFIRM images ship,
pointing at the eMMC env) and checks fw_setenv results (audit N16).
BUILD.md gets the real artifact name and marks the built u-boot
reference-only; INSTALL.md drops the stale script/ogboot names and the
cloud-connect promise, stating the image is bring-up-only (audit N11).
ScottW514