install-sdp-test-suite-run skill: document the manual real
install-then-upgrade testing procedure (DANGER_CLEAN.sh -> install
an older real release -> upgrade to the release candidate ->
verify), codifying what was proven out for real today catching
SDP-1394/1395. This fleet's automated suite (cli_tests.cfg/./r)
only exercises install_sdp.sh fresh installs, never
sdp_upgrade.sh -- flagged as a real, currently-unautomated gap
that let both bugs ship in 2026.1 GA. Recommends running this
manually as part of Step 4 (pre-release verification) for any
release touching the package-structure install/upgrade path, not
just post-release smoke testing.