chore(monorepo/server): move server-side source code

apps/server/src/etapi/spec.ts

@@ -0,0 +1,23 @@
+import type { Router } from "express";
+
+import fs from "fs";
+import path from "path";
+
+import { fileURLToPath } from "url";
+const specPath = path.join(path.dirname(fileURLToPath(import.meta.url)), "etapi.openapi.yaml");
+let spec: string | null = null;
+
+function register(router: Router) {
+    router.get("/etapi/etapi.openapi.yaml", (req, res, next) => {
+        if (!spec) {
+            spec = fs.readFileSync(specPath, "utf8");
+        }
+
+        res.header("Content-Type", "text/plain"); // so that it displays in browser
+        res.status(200).send(spec);
+    });
+}
+
+export default {
+    register
+};