docs: add Universal-3 Pro upgrade callout to Universal-2 code switching section

[devin-ai-integration]

Summary

Adds a <Note> callout to the Universal-2 subsection of the Code Switching page, recommending users upgrade to Universal-3 Pro if their use case involves code-switching between English, Spanish, Portuguese, French, German, or Italian.

The callout is placed after the Universal-2 section description and before the code examples.

Review & Testing Checklist for Human

• Verify the callout placement is correct — it appears between the Universal-2 intro text and the code blocks, which feels natural, but confirm this is where you want it
• Confirm the rendered <Note> component looks correct on the docs site (check the preview deployment)

Notes

• The <Note> component follows the same pattern used elsewhere in this file (e.g., the "Language support" note in the Universal-3 Pro section)
• Callout text was provided verbatim by the requester

Link to Devin session: https://app.devin.ai/sessions/98b57587842a4b71815206bc2b6e91b7
Requested by: @LeeVaughn

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