fix(config): add IDX configuration

.idx/dev.nix

@@ -0,0 +1,33 @@
+{ pkgs, ... }: {
+  channel = "stable-23.11";
+
+  packages = [
+    pkgs.nodejs_20
+  ];
+
+  services.mongodb = {
+    enable = true;
+  };
+
+  idx = {
+    extensions = [
+      "mongodb.mongodb-vscode"
+    ];
+
+    workspace = {
+      onCreate = {
+        npm-install = "npm install";
+        default.openFiles = [
+          "server.js" "database.js" "README.md"
+        ];
+      };
+      onStart = {
+        start-database = "mongod --port 27017 --fork --logpath ./.idx/database.log --dbpath ./.idx/.data";
+        run-server = "node server.js";
+      };
+    };
+
+    previews = {
+    };
+  };
+}