certs: rename /certified-partners path and add redirect for SEO

[frameworks-volunteer]

Summary

PR #520 reworked the Certified Partners page into an Auditor Accreditation page, but the URL path remains /certs/certified-partners and the sidebar label still reads "Certified Partners". This creates an SEO mismatch between the page content/title and its URL slug.

Tasks

1. Rename the page route from /certs/certified-partners to /certs/auditor-accreditation (or similar slug matching the new page title).
2. Update vocs.config.tsx sidebar entry (line 587) to use the new path and label "Auditor Accreditation".
3. Add a redirect from /certs/certified-partners → /certs/auditor-accreditation so existing links (including the SEAL website) continue to resolve.
4. Update any internal links across the docs that reference the old path.

Context

• PR certs: Auditor Accreditation page (replace Certified Partners RFQ) #520 changed the page content from "Certified Partners RFQ" to "Auditor Accreditation" but intentionally kept the old route to avoid breaking links.
• The redirect should be added before or at the same time as the rename so there is no downtime for existing inbound links.

References

• PR certs: Auditor Accreditation page (replace Certified Partners RFQ) #520: certs: Auditor Accreditation page (replace Certified Partners RFQ) #520