Add deprecation banner to Test Suites page

Adds a <Warning> deprecation banner to the Test Suites documentation
page informing users that Test Suites is being replaced by Simulations.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: betzlermeow

fern/test/test-suites.mdx

@@ -4,6 +4,10 @@ subtitle: End-to-end test automation for AI voice agents
 slug: /test/test-suites
 ---
 
+<Warning>
+Test Suites is being deprecated. It will be replaced by Simulations, a more powerful way to test your voice agents. You can keep using Test Suites in the meantime, and we'll share a migration guide once Simulations is ready.
+</Warning>
+
 ## Overview
 
 **Test Suite** is an end-to-end feature that automates testing of your AI voice agents. Our platform simulates an AI tester that interacts with your voice agent by following a pre-defined script. After the interaction, the transcript is sent to a language model (LLM) along with your evaluation rubric. The LLM then determines if the interaction met the defined objectives.