ci(evals): Add a Next.js-only eval label

ai-evals:nextjs:opus-5.5 runs only the Next.js products test, once getsentry/sentry-for-ai-evals#88 gives it a nextjs mark.

Refs VDY-307

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: jaydgoss

.github/labels.yml

@@ -291,6 +291,9 @@
 - name: 'ai-evals:products:opus-5.5'
   color: 6F42C1
   description: Run the products evals on Opus 5.5 only, on this PR's preview and the live docs
+- name: 'ai-evals:nextjs:opus-5.5'
+  color: 6F42C1
+  description: Run the Next.js products eval on Opus 5.5 only, on this PR's preview and the live docs
 
 # Miscellaneous
 - name: API Docs