Resolve all statix and nixpkgs-fmt warnings repo-wide

Zero W20 (repeated attribute keys), W10 (empty { ... }: variadic
pattern, use _: instead), and W04 (a = x.a instead of inherit)
warnings remain anywhere in the tree, and nixpkgs-fmt --check is
clean on all 46 .nix files.

Repeated-key merges go as deep as statix actually flags per file
(e.g. boot.loader.* nested under boot.loader = { ... } once the
outer boot.* merge exposed it as its own repeat) — every merge is a
pure attribute-path restructuring with no value changes, verified by
comparing config.system.build.toplevel.drvPath before/after for a
representative host per changed module plus a full 19-host + 4-package
eval sweep.

One indentation slip caught and fixed during this pass: nesting
modules/installer/common.nix's environment.etc."auto-install.sh".text
under an environment = { ... } block initially normalized the
script's shebang/set line indentation, which actually changes the
rendered file (Nix's '' string dedent treats it as real content, not
cosmetic whitespace) — reproduced the original's exact indentation
and reverified the rendered script is byte-identical to before.

modules/services/zfs/auto-mount-volumes.nix picked up formatting too;
worth noting it isn't imported by anything in this flake at all.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01La55Nsss8jZ7ZuzUV9mfot

modules/hardware-configuration/vm/proxmox.nix

@@ -5,13 +5,16 @@
 
 {
   imports =
-    [ (modulesPath + "/profiles/qemu-guest.nix")
+    [
+      (modulesPath + "/profiles/qemu-guest.nix")
     ];
 
-  boot.initrd.availableKernelModules = [ "ata_piix" "uhci_hcd" "virtio_pci" "virtio_scsi" "sd_mod" "sr_mod" ];
-  boot.initrd.kernelModules = [ ];
-  boot.kernelModules = [ "kvm-amd" ];
-  boot.extraModulePackages = [ ];
+  boot = {
+    initrd.availableKernelModules = [ "ata_piix" "uhci_hcd" "virtio_pci" "virtio_scsi" "sd_mod" "sr_mod" ];
+    initrd.kernelModules = [ ];
+    kernelModules = [ "kvm-amd" ];
+    extraModulePackages = [ ];
+  };
   # boot.loader.grub.device = "/dev/sda2"; # or "nodev" for efi only
 
   # fileSystems."/" =