docs: fix moved Continue.dev roles guide link - #1487

Summary

The Continue.dev docs moved their roles guide. https://docs.continue.dev/customize/model-roles/intro now returns 404, and the page is served at https://docs.continue.dev/customize/model-roles/00-intro ("Intro to Roles"). This updates the single link in the Continue.dev tutorial so readers can still reach the roles guide.

Related issue or discussion

None.

Checklist

• I have reviewed the relevant documentation and matched the existing style.
• This PR meets Open WebUI's contribution standards: it is accurate, relevant to users, narrowly scoped, maintainable, and not promotional content, advertising, lead generation, SEO placement, or a request to list a product, service, provider, integration, gateway, tool, or company primarily for visibility.
• I understand that PRs that do not meet these standards may be closed without review and will not be merged. Repeated, low-quality, off-topic, promotional, or intentionally misleading submissions may result in the contributor being blocked from future participation in Open WebUI repositories.

Notes for reviewers

Link target only, no wording changes. The old URL returns 404 and the new URL returns 200 with the title "Intro to Roles". This is the only page in the docs that links to customize/model-roles.