feat(server): bump models (#15013)

#### PR Dependency Tree


* **PR #15013** 👈

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## Summary by CodeRabbit

* **New Features**
* Expanded AI capabilities with the addition of Gemini 3.5 Flash model,
providing enhanced options for AI-powered features.

* **Updates**
* Updated Claude Sonnet to the latest version for improved performance.
  * Refreshed pro models configuration with optimized selections.

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packages/backend/native/src/llm/assets/prompts/built-in.json

@@ -706,8 +706,8 @@
     "optionalModels": [
       "gemini-2.5-flash",
       "gemini-2.5-pro",
-      "gemini-3.1-pro-preview",
-      "claude-sonnet-4-5@20250929"
+      "gemini-3.5-flash",
+      "claude-sonnet-4-6"
     ],
     "config": {
       "tools": [
@@ -722,11 +722,7 @@
         "codeArtifact",
         "blobRead"
       ],
-      "proModels": [
-        "gemini-2.5-pro",
-        "gemini-3.1-pro-preview",
-        "claude-sonnet-4-5@20250929"
-      ]
+      "proModels": ["gemini-2.5-pro", "gemini-3.5-flash", "claude-sonnet-4-6"]
     },
     "builtins": [
       "date",

packages/backend/native/src/llm/core/model_registry.rs

@@ -61,12 +61,12 @@ mod tests {
   fn should_resolve_backend_scoped_alias() {
     let response = llm_resolve_model_registry_variant(ModelRegistryResolveRequest {
       backend_kind: Some("anthropic_vertex".to_string()),
-      model_id: "claude-sonnet-4.5".to_string(),
+      model_id: "claude-sonnet-4.6".to_string(),
     })
     .unwrap();
 
     assert_eq!(response.matched_by.as_deref(), Some("canonical"));
-    assert_eq!(response.variant.unwrap().raw_model_id, "claude-sonnet-4-5@20250929");
+    assert_eq!(response.variant.unwrap().raw_model_id, "claude-sonnet-4-6");
   }
 
   #[test]