feat(nix): initialize flake with basic structure

Add flake.nix with nixpkgs and flake-utils inputs.
This provides the foundation for building a Neovim package
that can be referenced in home-manager configurations.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

flake.nix

@@ -0,0 +1,18 @@
+{
+  description = "Personal Neovim configuration based on kickstart.nvim";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+      {
+        # Outputs will be added in subsequent commits
+      }
+    );
+}