feat(openapi): Add OpenAPI module: decorators, spec generator, runtime validation and Swagger UI

ts/decorators/decorators.metadata.ts

@@ -135,7 +135,7 @@ export function combinePaths(basePath: string, routePath: string): string {
   const route = normalizePath(routePath);
 
   if (!base) return route || '/';
-  if (!route) return base;
+  if (!route || route === '/') return base || '/';
 
   return `${base}${route}`;
 }