improvements(ai): Improve AI streaming UI/UX interactions + better separation of AI provider responsibilities (#2039)

* Start refactor

* Interface updates

* Rework Assistant, Provider, and tests for better domain boundaries

* Consolidate and simplify OpenAI provider and provider concepts

* Clean up assistant streaming

* Improve assistant message orchestration logic

* Clean up "thinking" UI interactions

* Remove stale class

* Regenerate VCR test responses

app/models/assistant/function.rb

@@ -34,6 +34,15 @@ class Assistant::Function
     true
   end
 
+  def to_definition
+    {
+      name: name,
+      description: description,
+      params_schema: params_schema,
+      strict: strict_mode?
+    }
+  end
+
   private
     attr_reader :user