Systems installed before vulkan.sh (2026-02-20) never received their Mesa
Vulkan ICD. Add a migration replaying vulkan.sh's GPU vendor detection and
idempotent omarchy-pkg-add calls to backfill Intel/AMD/Asahi drivers.
Closes#6199. Reported in #6089.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
