fix Pi build and CI pipeline ordering

- Fix Pi kernel build: disable includeDefaultModules in initrd.
  NixOS all-hardware.nix includes dw-hdmi which doesn't exist in
  the RPi4 kernel 6.12, causing module-shrunk to fail.
- Fix CI: SD image build now depends on build-hosts instead of
  flake-check, so it won't run if the Pi build fails.
- Apply same fix to raspberry-pi template.

templates/raspberry-pi/hardware.nix

@@ -3,11 +3,15 @@
 {
   boot = {
     kernelPackages = pkgs.linuxKernel.packages.linux_rpi4;
-    initrd.availableKernelModules = [
-      "xhci_pci"
-      "usbhid"
-      "usb_storage"
-    ];
+    initrd = {
+      availableKernelModules = [
+        "xhci_pci"
+        "usbhid"
+        "usb_storage"
+      ];
+      # Disable default x86 modules that don't exist in the Pi kernel (e.g. dw-hdmi)
+      includeDefaultModules = false;
+    };
   };
 
   fileSystems = {