Add basic nix package

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -1 +1,2 @@
 /target
+/.direnv

flake.lock

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+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1731245184,
+        "narHash": "sha256-vmLS8+x+gHRv1yzj3n+GTAEObwmhxmkkukB2DwtJRdU=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "aebe249544837ce42588aa4b2e7972222ba12e8f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+  };
+
+  outputs = { self, nixpkgs }:
+    let pkgs = nixpkgs.legacyPackages.x86_64-linux;
+    inherit (pkgs) lib;
+    system = "x86_64-linux";
+    in rec {
+      formatter."${system}" = pkgs.nixfmt-rfc-style;
+      devShells."${system}".default = pkgs.mkShell {
+        packages = [
+          pkgs.mkvtoolnix-cli
+        ];
+      };
+
+      overlays.default = final: prev: {
+        subtitle-merge = final.rustPlatform.buildRustPackage {
+          name = "subtitle-merge";
+          version = "1.0";
+          src = ./.;
+          cargoLock.lockFile = ./Cargo.lock;
+          buildInputs = [ final.mkvtoolnix-cli ];
+        };
+      };
+
+      packages."${system}" = rec {
+        subtitle-merge = (overlays.default pkgs pkgs).subtitle-merge;
+        default = subtitle-merge;
+      };
+    };
+}