fix(common): set mutableUsers = false to fix password setup on disk images

When a proxmox-* disk image is built, activation runs during the image
build without a valid sops age key (the SSH host key doesn't exist yet),
so root and nixos land in /etc/shadow with locked '!' entries. With the
default mutableUsers = true, update-users-groups.pl preserves existing
shadow entries for accounts that already exist, so hashedPasswordFile is
silently ignored on every subsequent boot — passwords are never fixed.

Setting mutableUsers = false forces update-users-groups.pl to apply
hashedPasswordFile unconditionally on every activation. On first real
boot the sops-decrypted hash is now written regardless of whether the
account already existed in shadow from the image build.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011uRcikkTp3D5VbXj2DwNpQ

modules/common/configuration.nix

@@ -61,24 +61,32 @@
     !include ${config.sops.templates."nix-github-token.conf".path}
   '';
 
-  #Set root password
-  users.users.root = {
-    hashedPasswordFile = config.sops.secrets."root-hashedPassword".path;
-  };
+  users = {
+    # With mutableUsers = false, update-users-groups.pl enforces hashedPasswordFile
+    # on every activation regardless of whether the account already exists in
+    # /etc/shadow. The default (true) only applies hashedPasswordFile to newly-
+    # created accounts — which means a freshly-built proxmox disk image (where
+    # activation runs without a usable sops key, so both accounts land in shadow
+    # with ‘!’) will never have its passwords fixed by subsequent boots.
+    mutableUsers = false;
 
-  # Define a user account. Don't forget to set a password with ‘passwd’.
-  users.users.${vars.primaryUser} = {
-    isNormalUser = true;
-    extraGroups = [ "wheel" ]; # Enable ‘sudo’ for the user.
-    packages = with pkgs; [
-      tree
-    ];
-    hashedPasswordFile = config.sops.secrets."nixos-hashedPassword".path;
-    openssh.authorizedKeys.keys = [
-      vars.adminSshKey
-      "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAICMJhrfFayLBG+gWtO6oAvgambw5nWWgztiTFEaaaVRH debian@surface"
-      "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIGygkCljN6uKpdJbHTOQtn8ZnH+wKXDLAwrDFbLrE/65 nixos@nixos"
-    ];
+    users.root = {
+      hashedPasswordFile = config.sops.secrets."root-hashedPassword".path;
+    };
+
+    users.${vars.primaryUser} = {
+      isNormalUser = true;
+      extraGroups = [ "wheel" ]; # Enable ‘sudo’ for the user.
+      packages = with pkgs; [
+        tree
+      ];
+      hashedPasswordFile = config.sops.secrets."nixos-hashedPassword".path;
+      openssh.authorizedKeys.keys = [
+        vars.adminSshKey
+        "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAICMJhrfFayLBG+gWtO6oAvgambw5nWWgztiTFEaaaVRH debian@surface"
+        "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIGygkCljN6uKpdJbHTOQtn8ZnH+wKXDLAwrDFbLrE/65 nixos@nixos"
+      ];
+    };
   };