fix: infer --auth-choice from API key flags during non-interactive onboarding (#9241)

* fix: infer --auth-choice from API key flags during non-interactive onboarding

When --anthropic-api-key (or other provider key flags) is passed without
an explicit --auth-choice, the auth choice defaults to "skip", silently
discarding the API key. This means the gateway starts without credentials
and fails on every inbound message with "No API key found for provider".

Add inferAuthChoiceFromFlags() to derive the correct auth choice from
whichever provider API key flag was supplied, so credentials are persisted
to auth-profiles.json as expected.

Fixes #8481

* fix: infer auth choice from API key flags (#8484) (thanks @f-trycua)

* refactor: centralize auth choice inference flags (#8484) (thanks @f-trycua)

---------

Co-authored-by: f-trycua <f@trycua.com>

CHANGELOG.md

@@ -30,6 +30,7 @@ Docs: https://docs.openclaw.ai
 - Web UI: fix agent model selection saves for default/non-default agents and wrap long workspace paths. Thanks @Takhoffman.
 - Web UI: resolve header logo path when `gateway.controlUi.basePath` is set. (#7178) Thanks @Yeom-JinHo.
 - Web UI: apply button styling to the new-messages indicator.
+- Onboarding: infer auth choice from non-interactive API key flags. (#8484) Thanks @f-trycua.
 - Security: keep untrusted channel metadata out of system prompts (Slack/Discord). Thanks @KonstantinMirin.
 - Security: enforce sandboxed media paths for message tool attachments. (#9182) Thanks @victormier.
 - Security: require explicit credentials for gateway URL overrides to prevent credential leakage. (#8113) Thanks @victormier.