fix: remove redundant error handling for project root detection

tools/flattener/main.js

@@ -127,11 +127,6 @@ program
           path.join(inputDir, "flattened-codebase.xml"),
         );
       }
-    } else {
-      console.error(
-        "Could not auto-detect a project root and no arguments were provided. Please specify -i/--input and -o/--output.\nRefer to the documentation in the [https://github.com/bmad-code-org/BMAD-METHOD/tree/main?tab=readme-ov-file#codebase-flattener-tool](https://github.com/bmad-code-org/BMAD-METHOD/tree/main?tab=readme-ov-file#codebase-flattener-tool) (ReadMe)",
-      );
-      process.exit(1);
     }
 
     // Ensure output directory exists