feat: add Open GameStudio Codex port

docs/setup.md

@@ -0,0 +1,26 @@
+# Setup
+
+Install and verify with Node 20 or newer:
+
+```bash
+npm install
+npm run typecheck
+npm run build
+npm test
+npm run validate
+```
+
+Local development scripts build first and then run `node dist/cli.js`.
+
+```bash
+npm run init -- --name "My Game" --engine godot --mode prototype --non-interactive --competitor "Mini Metro" --engine-version "4.4.1"
+npm run templates -- list
+npm run validate -- --project projects/my-game
+```
+
+After build/link/install, the package bin is available:
+
+```bash
+npm exec open-gamestudio -- --help
+npm exec open-gamestudio -- templates show gdd
+```