Add EU endpoint support via base_url to LiveKit pages

[devin-ai-integration]

Add EU endpoint support via base_url to LiveKit pages

Summary

Documents EU endpoint support via the base_url parameter on both LiveKit-related documentation pages:

• LiveKit intro guide (livekit-intro-guide.mdx): New "EU endpoint" section added before "Production Deployment" with a full code example including turn detection params.
• LiveKit integration page (voice-agents/livekit.mdx): New "EU endpoint" subsection under Configuration, plus base_url added to the Parameters reference list.

Both sections link back to the existing Select the region page for further details.

Local Testing

Verified both pages render correctly via fern docs dev. The EU endpoint section, code snippet, and parameter reference all display as expected:

Note: CI failures (fern-check, lint) are pre-existing on main and unrelated to these changes. The [docs]:✓ All checks passed check confirms docs validation passes.

Review & Testing Checklist for Human

• Verify base_url is the correct parameter name for assemblyai.STT() in the LiveKit Agents plugin. The existing "Select the region" page uses api_host for the Python SDK's StreamingClientOptions — confirm these are intentionally different interfaces.
• Confirm the EU URL wss://streaming.eu.assemblyai.com is correct for the LiveKit integration context (matches what was requested in the Slack thread).
• Test the internal link to "Select the region" resolves correctly in production (during local dev, the URL routing differed slightly from the defined path).
• Run fern docs dev and spot-check both pages render correctly end-to-end.

Notes

• Requested by: Dan Ince
• Link to Devin run

[devin-ai-integration]

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