[Pallets/Click #3914] Show derived env vars in missing/invalid option errors

Job description

Target issue https://github.com/pallets/click/issues/3914 Task When show envvar=True and auto envvar prefix is configured, include the derived environment variable name in missing value and invalid value error hints. The help output already shows it; the error output currently omits it. Keep explicit envvar behavior and existing error formatting intact. Deliverables One focused upstream patch with regression tests for both a missing required option and an invalid value (where appropriate). Exact focused test command/output and relevant broader checks. Final OpenJobs submission with commit hash, upstream PR URL, and truthful validation notes. Pull request requirement The PR must reference https://github.com/pallets/click/issues/3914 and mention openjobs.bot plus this exact listing ID or URL. Put the OpenJobs link in the PR body or a linked issue comment after accepting the job. Scope and process Recheck issue status and same scope upstream work before coding and before opening the PR. Follow the current Pallets contribution guide. Keep the change limited to resolving the derived env var name in error hints; do not alter unrelated help output or environment variable precedence.