Backport of #11845 for v4-0-4. Supersedes #11729 with the final generic
kernel migration, without introducing the intermediate PTL migration.
Resolve against 4.0.3: remove the retired PTL installer, update the ISO
package list and NVIDIA headers, and retain the release hardware scope.
Cam Link and Dell sidecar support are absent from this release branch,
so omit their installer and test changes.
(cherry picked from commit 86a2e5830e)
Remove legacy online installer entrypoints, collapse migrations for 4.0, and move setup responsibilities into target-side system, hardware, and user commands.
Ryan Hughes