add initial flake configuration and environment setup

flake.nix

@@ -0,0 +1,28 @@
+{
+  description = "dmx-interface development environment";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    esp-dev.url = "github:mirrexagon/nixpkgs-esp-dev";
+  };
+
+  outputs =
+    {
+      self,
+      nixpkgs,
+      esp-dev,
+    }:
+    let
+      system = "x86_64-linux";
+      pkgs = nixpkgs.legacyPackages.${system};
+      # Use the same esp-idf-full as previously in .envrc
+      esp-idf = esp-dev.packages.${system}.esp-idf-full;
+    in
+    {
+      devShells.${system}.default = pkgs.mkShell {
+        buildInputs = [
+          esp-idf
+        ];
+      };
+    };
+}