fix(cli): respect existing config during onboarding

[cyphercodes]

Description

Fixes #12258.

• Skip CLI onboarding prompts when the default ~/.continue/config.yaml already exists, allowing the normal config loader to use an existing local config.
• Mark onboarding complete after a successful explicit --config load so one-time config selection is remembered.
• Add unit coverage for both local default config skipping and successful --config completion marking.

AI Code Review

• Team members only: AI review runs automatically when PR is opened or marked ready for review
• Team members can also trigger a review by commenting @continue-review

Checklist

• I've read the contributing guide
• The relevant docs, if any, have been updated or created
• The relevant tests, if any, have been updated or created

Screen recording or screenshot

N/A — CLI onboarding behavior is covered by unit tests.

Tests

• npm test -- src/onboarding.test.ts
• npx prettier --check src/onboarding.ts src/onboarding.test.ts
• npm run lint
• npm run build
• git diff --check

---

Summary by cubic

Skips CLI onboarding when a local config exists and persists successful --config loads so users aren't prompted again.

• Bug Fixes
  • Skip interactive onboarding if ~/.continue/config.yaml exists; use the normal loader.
  • After a successful --config load, mark onboarding complete so the choice persists.

^{Written for commit adf565f. Summary will update on new commits. Review in cubic}

[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

---

_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}

[cubic-dev-ai]

No issues found across 2 files