#16626: fix: prompt onboarding auth selection when auth choice is blank

## Describe your changes - Normalize onboarding auth-related CLI inputs so blank `--auth-choice` values are treated as unset. - Ensure interactive onboarding still opens the model/auth provider prompt when auth choice is empty/whitespace, instead of skipping straight to channels. - Add regression tests for option normalization, wizard auth prompting with blank auth choice, and CLI smoke coverage for blank auth choice forwarding. ## Screenshot or video (only for visual changes) - N/A ## GitHub Issue Link (if applicable) - https://github.com/openclaw/openclaw/issues/16579 ## Testing Plan - Explanation of why no additional tests are needed: Covered by targeted unit and e2e smoke tests in this PR. - Unit Tests (JS and/or Python): `pnpm test src/commands/onboard-option-normalization.test.ts src/wizard/onboarding.test.ts` - E2E Tests: `pnpm test:e2e src/cli/program.smoke.e2e.test.ts` - Any manual testing needed?: Optional: run `openclaw onboard` and confirm provider/auth prompt appears before channel setup. --- **Contribution License Agreement** By submitting this pull request you agree that all contributions to this project are made under the Apache 2.0 license.