feat(nixos): migrate system configuration

configs/nixos/hosts/neogaia/disk.nix

@@ -0,0 +1,63 @@
+{ ... }:
+# neogaia's disk layout for disko: one NVMe disk, GPT, with an EFI system
+# partition and a LUKS container holding btrfs subvolumes.
+# No swap partition, since swap is zram.
+# disko derives `fileSystems` and `boot.initrd.luks.devices` from this.
+{
+  disko.devices.disk.main = {
+    type = "disk";
+    device = "/dev/nvme0n1";
+    content = {
+      type = "gpt";
+      partitions = {
+        ESP = {
+          # Each generation stores a kernel and initrd here and the CachyOS kernel is large.
+          # An exhausted partition fails bootloader installs.
+          size = "2G";
+          type = "EF00";
+          content = {
+            type = "filesystem";
+            format = "vfat";
+            mountpoint = "/boot";
+            mountOptions = [ "umask=0077" ];
+          };
+        };
+        luks = {
+          size = "100%";
+          content = {
+            type = "luks";
+            name = "cryptroot";
+            settings.allowDiscards = true;
+            content = {
+              type = "btrfs";
+              extraArgs = [ "-f" ];
+              subvolumes = {
+                "@root" = {
+                  mountpoint = "/";
+                  mountOptions = [
+                    "compress=zstd"
+                    "noatime"
+                  ];
+                };
+                "@home" = {
+                  mountpoint = "/home";
+                  mountOptions = [
+                    "compress=zstd"
+                    "noatime"
+                  ];
+                };
+                "@nix" = {
+                  mountpoint = "/nix";
+                  mountOptions = [
+                    "compress=zstd"
+                    "noatime"
+                  ];
+                };
+              };
+            };
+          };
+        };
+      };
+    };
+  };
+}