docs: Adds redirects for deleted topic

[Dan-Heath]

Description

In PR #3444 , we deleted two deprecated pages:

• The api-clients overview page has been deprecated and hidden from the TOC since the IA reorg in v0.19.x. The page contained no useful information and was basically a placeholder.
• The legacy Boundary Desktop has been hidden from the TOC since before v0.13.x.

This PR creates redirects from the api-clients overview to the Boundary API overview page for the deprecated versions v0.19.x - v0.21.x and the current version. It also creates a redirect in the current version from the legacy Boundary Desktop topic to the new Boundary Desktop Client topic.

To test the redirects, verify that the following links redirect to the Boundary API overview page:

• https://unified-docs-frontend-preview-pr-3533-hashicorp.vercel.app/boundary/docs/api-clients
• https://unified-docs-frontend-preview-pr-3533-hashicorp.vercel.app/boundary/docs/v0.21.x/api-clients
• https://unified-docs-frontend-preview-pr-3533-hashicorp.vercel.app/boundary/docs/v0.20.x/api-clients
• https://unified-docs-frontend-preview-pr-3533-hashicorp.vercel.app/boundary/docs/v0.19.x/api-clients

And verify that the following link redirects to the new Boundary Desktop Client topic:

• https://unified-docs-frontend-preview-pr-3533-hashicorp.vercel.app/boundary/docs/api-clients/desktop

Links

Code PR:
Jira:
GitHub issue:
RFC/PRD:

Contributor checklists

Review urgency:

• ASAP: Bug fixes, broken content, imminent releases
• 3 days: Small changes, easy reviews
• 1 week: Default expectation
• Best effort: No urgency

Pull request:

• Verify that the PR is set to merge into the correct base branch
• Verify that all status checks passed
• Verify that the preview environment deployed successfully
• Add additional reviewers if they are not part of assigned groups

Content:

• I added redirects for any moved or removed pages
• I kept this PR to one docs set and did not combine moved or renamed pages with rewrites, or I explained why in the description. Refer to Keep changes reviewable.
• I followed the Education style guide
• I looked at the local or Vercel build to make sure the content rendered correctly

[github-actions]

Vercel Previews Deployed

Name	Status	Preview	Updated (UTC)
Dev Portal	✅ Ready (Inspect)	Visit Preview	Wed Sep 23 15:38:54 UTC 2026
Unified Docs API	✅ Ready (Inspect)	Visit Preview	Wed Sep 23 15:34:06 UTC 2026

[github-actions]

Broken Link Checker

This PR contains broken links, but won't be blocked. Use this report to improve content quality:

Quick Actions

• Internal links (HashiCorp sites): Please fix these - they impact user experience
• External links: Consider if these are essential or can be updated/removed
• Temporary issues: External sites may recover - check again before merging

Need Help?

• Review our Broken Link Monitoring docs
• Check the monthly production report for context

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Internal Links

Full Github Actions output

External Links

Summary

Status	Count
🔍 Total	46
✅ Successful	0
⏳ Timeouts	0
🔀 Redirected	0
👻 Excluded	46
❓ Unknown	0
🚫 Errors	0
⛔ Unsupported	0

Full Github Actions output

[stellarsquall]

looks good!