feat: add _health route

proxy/gen-routes.ts

···
   routeImports.push(`import ${routeName}Route from "./${routeName}";`);
 
   // Generate route map entry
-  routeMap.push(`  "${routePath}": ${routeName}Route,`);
+  routeMap.push(`  "${routePath}": ${routeName}Route`);
 }
 
 // Generate the complete index.ts content

proxy/src/routes/_health.ts

···
+const GET = async (req: Bun.BunRequest) => {
+  return new Response(JSON.stringify({ version: "0.1.0" }));
+};
+
+export default { GET };

proxy/src/routes/index.ts

···
 // Auto-generated route index
+import _healthRoute from "./_health";
 import pushRoute from "./push";
 
 export const routes = {
-  "/push": pushRoute,
+  "/_health": _healthRoute,
+  "/push": pushRoute
 };
 
 export default routes;