refactor: reorganize directory structure (variants -> hw, glue -> fleet)

- Rename variants/ to hw/ for clearer hardware module naming
- Rename glue/ to fleet/ for more intuitive fleet management
- Move boot/fs configuration from glue/boot.nix to separate fleet/boot.nix and fleet/fs.nix
- Improve separation of concerns between boot, filesystem, and common config

fleet/fs.nix

@@ -0,0 +1,90 @@
+# ============================================================================
+# FS & Storage Configuration
+# ============================================================================
+# This module defines:
+# - Disko partition layout (EFI, swap, root)
+# - Filesystem options (device, swap size)
+
+{ config, lib, ... }:
+
+{
+  options.athenix = {
+    host.filesystem = {
+      device = lib.mkOption {
+        type = lib.types.nullOr lib.types.str;
+        default = null;
+        description = "The main disk device to use for installation.";
+      };
+      useSwap = lib.mkOption {
+        type = lib.types.bool;
+        default = true;
+        description = "Whether to create and use a swap partition.";
+      };
+      swapSize = lib.mkOption {
+        type = lib.types.nullOr lib.types.str;
+        default = null;
+        description = "The size of the swap partition.";
+      };
+    };
+  };
+
+  config = {
+    # ========== Disk Partitioning (Disko) ==========
+    disko.enableConfig = lib.mkDefault (config.athenix.host.filesystem.device != null);
+
+    disko.devices = {
+      disk.main = {
+        type = "disk";
+        device = config.athenix.host.filesystem.device;
+        content = {
+          type = "gpt";
+          partitions = {
+            # EFI System Partition
+            ESP = {
+              name = "ESP";
+              label = "BOOT";
+              size = "1G";
+              type = "EF00";
+              content = {
+                type = "filesystem";
+                format = "vfat";
+                mountpoint = "/boot";
+                mountOptions = [ "umask=0077" ];
+                extraArgs = [
+                  "-n"
+                  "BOOT"
+                ];
+              };
+            };
+
+            # Swap Partition (size configurable per host)
+            swap = lib.mkIf config.athenix.host.filesystem.useSwap {
+              name = "swap";
+              label = "swap";
+              size = config.athenix.host.filesystem.swapSize;
+              content = {
+                type = "swap";
+              };
+            };
+
+            # Root Partition (takes remaining space)
+            root = {
+              name = "root";
+              label = "root";
+              size = "100%";
+              content = {
+                type = "filesystem";
+                format = "ext4";
+                mountpoint = "/";
+                extraArgs = [
+                  "-L"
+                  "ROOT"
+                ];
+              };
+            };
+          };
+        };
+      };
+    };
+  };
+}