Add redirects for content-safety-detection and real-time-transcription URLs

[devin-ai-integration]

Summary

Adds two URL redirects to handle old documentation URLs:

• /docs/guides/content-safety-detection → /docs/content-moderation
• /docs/overview/real-time-transcription → /docs/universal-streaming

No instances of these old URLs were found in the codebase itself, so this change only adds redirects for any external links pointing to these deprecated paths.

Updates since last revision

• Reverted back to relative URL format (/docs/...) per reviewer feedback

Review & Testing Checklist for Human

• Confirm the destination URLs (/docs/content-moderation and /docs/universal-streaming) are the correct targets
• After deployment, test that visiting the old URLs properly redirects to the new destinations

Notes

• CI failures (lint, fern-check) are pre-existing issues in openapi.yml that also fail on main branch; unrelated to this redirect-only change
• Requested by Griffin Sharp (@gsharp-aai) via Slack #ask-api-docs
• Link to Devin run: https://app.devin.ai/sessions/f562da3cbeb34a409bc67a17c2d68f39

[devin-ai-integration]

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