chore: Friendly error text when routes are not found

Currently, when in Standalone configuration and Route is not found, the following error is displayed

> Could not find your routes file. Use the skip-import option to skip importing.

The toolkit knows if a route file is a route file if the naming convention matches /.routes\.ts/. However, the file name can be changed at will. So, how about adding a sentence to the error statement such as "routes files are detected based on whether they match /.routes\.ts/"?

Search the codebase for the exact error text "Could not find your routes file" and inspect the standalone route-file detection path. Update the message to explain that route files are detected by the /.routes\.ts/ naming convention, then run the relevant existing tests if available to verify the wording.

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