Treat matching kernel headers as a base system guarantee

(cherry picked from commit 24417bf191)

agents/skills/install-scripts.md

@@ -13,6 +13,7 @@ commands and reusable setup leaves:
 - use `$OMARCHY_INSTALL` and `$OMARCHY_PATH` instead of hard-coded Omarchy paths.
 - keep root-scoped hardware setup under `install/hardware/` and orchestrate it through `install/hardware/all.sh`.
 - keep every per-user setup leaf under `install/user/` (including `install/user/hardware/` and `install/user/first-run/`) so it is clear what must run for each user.
+- The base install supplies matching kernel headers before hardware setup. DKMS installers should install their driver packages and assume the headers exist.
 - prefer helper commands for package and command checks where available.
 
 Raw `command -v`, `pacman`, and `pacman-key` are acceptable in package-helper