refactor(installer): extract validate_yesno and a NVIDIA driver-floor constant

Four near-identical blocks validated that AUTOLOGIN, NO_GPU_DRIVERS, INSTALL_CLAUDE_CODE, and INSTALL_DEVICE_UDEV_RULES were empty or exactly yes/no. They collapse into a validate_yesno helper the callers guard with `|| exit 1`.

The NVIDIA driver floor of 535 was a magic literal in the comparison and three prose lines. It now lives in a NVIDIA_MIN_DRIVER constant, and the nvidia-preflight test sources that constant alongside the function it extracts.

This is the safe, purely-testable slice of the refactor rollup. The structural extractions that touch the installer's system-mutation paths -- the GPU modalias scan, the stow and retry loops, the display-server/window-manager dispatch, and the snapper/fsck/GRUB/waybar sed blocks -- are split into a follow-up so they get characterization coverage first rather than a blind rewrite.

1 files changed, 2 insertions, 1 deletions

diff --git a/tests/nvidia-preflight/test_nvidia_preflight.py b/tests/nvidia-preflight/test_nvidia_preflight.py
index bdacfd5..191e983 100644
--- a/tests/nvidia-preflight/test_nvidia_preflight.py
+++ b/tests/nvidia-preflight/test_nvidia_preflight.py
@@ -50,7 +50,8 @@ class NvidiaPreflightHarness(unittest.TestCase):
                 "#!/bin/bash\n"
                 'ARCHSETUP="$1"; shift\n'
                 "source <(sed -n "
-                "'/^nvidia_preflight_report() {/,/^}/p' \"$ARCHSETUP\")\n"
+                "'/^NVIDIA_MIN_DRIVER=/p;"
+                "/^nvidia_preflight_report() {/,/^}/p' \"$ARCHSETUP\")\n"
                 "nvidia_preflight_report\n"
             )
         os.chmod(self.wrapper, 0o755)