DEV: hide hyde model setting

Author: keegangeorge

config/settings.yml

@@ -267,6 +267,7 @@ discourse_ai:
     validator: "DiscourseAi::Configuration::LlmDependencyValidator"
     area: "ai-features/embeddings"
   ai_embeddings_semantic_search_hyde_model:  # Deprecated. TODO(keegan): Remove 2025-09-01
+    hidden: true
     default: ""
     type: enum
     allow_any: false