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

flake.nix

@@ -4,7 +4,7 @@
   # ============================================================================
   # This file defines the inputs (dependencies) and outputs (configurations)
   # for Athenix. It ties together the hardware, software, and user
-  # configurations into deployable systems.
+  # configurations into deployable systems using flake-parts.
 
   inputs = {
     # Core NixOS package repository (Release 25.11)
@@ -13,6 +13,12 @@
     # Older kernel packages for Surface compatibility if needed
     nixpkgs-old-kernel.url = "github:NixOS/nixpkgs/nixos-25.05";
 
+    # Flake-parts for modular flake organization
+    flake-parts = {
+      url = "github:hercules-ci/flake-parts";
+      inputs.nixpkgs-lib.follows = "nixpkgs";
+    };
+
     # Home Manager for user environment management
     home-manager = {
       url = "github:nix-community/home-manager/release-25.11";
@@ -54,51 +60,27 @@
       inputs.nixpkgs.follows = "nixpkgs";
     };
   };
+
   outputs =
-    inputs@{
-      self,
-      nixpkgs,
-      nixpkgs-old-kernel,
-      home-manager,
-      disko,
-      agenix,
-      lazyvim-nixvim,
-      nixos-hardware,
-      vscode-server,
-      nixos-generators,
-      ...
-    }:
-    let
-      fleet = self.lib.mkFleet { inherit inputs; };
-      linuxSystem = "x86_64-linux";
-      artifacts = import ./installer/artifacts.nix {
-        inherit inputs fleet self;
-        system = linuxSystem;
-      };
-      forAllSystems = nixpkgs.lib.genAttrs [
+    inputs@{ flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      # Support all common systems
+      systems = [
         "x86_64-linux"
         "aarch64-linux"
         "x86_64-darwin"
         "aarch64-darwin"
       ];
-    in
-    {
-      # Formatter for 'nix fmt'
-      formatter = forAllSystems (system: nixpkgs.legacyPackages.${system}.nixfmt-rfc-style);
 
-      # Generate NixOS configurations from fleet generator
-      nixosConfigurations = fleet.nixosConfigurations;
-
-      # Expose artifacts to all systems, but they are always built for x86_64-linux
-      packages.${linuxSystem} = artifacts;
-
-      # Expose host type modules and installer modules for external use
-      nixosModules = import ./installer/modules.nix { inherit inputs; };
-
-      # Library functions
-      lib = import ./lib { inherit inputs; };
-
-      # Templates for external configurations
-      templates = import ./templates;
+      # Import flake-parts modules
+      imports = [
+        ./parts/formatter.nix
+        ./parts/lib.nix
+        ./parts/fleet-data.nix
+        ./parts/nixos-configurations.nix
+        ./parts/nixos-modules.nix
+        ./parts/packages.nix
+        ./parts/templates.nix
+      ];
     };
 }