fix: Remove incorrect ./parts/fleet-data.nix import from flake.nix and use correct flake-parts structure

fleet/fleet-data.nix

@@ -0,0 +1,65 @@
+# ============================================================================
+# Fleet Data for NixOS Configurations
+# ============================================================================
+# This module exposes only the fleet inventory data (not hwTypes module functions)
+# to individual NixOS configurations. Used by fleet/common.nix.
+{ inputs, lib, ... }:
+let
+  fleetDefinition = lib.mkOption {
+    description = "Hardware types definitions for the fleet.";
+    type = lib.types.attrsOf (
+      lib.types.submodule (
+        { name, ... }:
+        {
+          options = {
+            type = lib.mkOption {
+              type = lib.types.oneOf [
+                lib.types.str
+                lib.types.listOf lib.types.str
+              ];
+              default = name;
+              description = "Type(s) of system configuration for this device.";
+            };
+            system = lib.mkOption {
+              type = lib.types.str;
+              default = "x86_64-linux";
+              description = "NixOS system architecture for this hardware type.";
+            };
+            devices = lib.mkOption {
+              type = lib.types.oneOf [
+                lib.types.int
+                (lib.types.attrsOf (
+                  lib.types.submodule (
+                    { name, ... }:
+                    {
+                      freeformType = lib.types.attrs;
+                    }
+                  )
+                ))
+              ];
+            };
+            count = lib.mkOption {
+              type = lib.types.int;
+              default = 0;
+              description = "Number of devices of this type to create.";
+            };
+            defaultCount = lib.mkOption {
+              type = lib.types.int;
+              default = 0;
+              description = "Default number of devices to create with default configurations and numbered hostnames.";
+            };
+            overrides = lib.mkOption {
+              type = lib.types.attrs;
+              default = { };
+              description = "Overrides to apply to all devices of this type.";
+            };
+          };
+        }
+      )
+    );
+  };
+in
+{
+  imports = [ ../inventory.nix ];
+  options.athenix.fleet = fleetDefinition;
+}