fix(google): add missing gemini-3.1-flash-lite to google-vertex catalog (#89400)

* fix(google): add gemini-3.1-flash-lite to provider catalog

Adds the missing gemini-3.1-flash-lite model definition to the
GOOGLE_GEMINI_TEXT_MODELS array. This resolves the ProviderFailoverError
when configuring google-vertex/gemini-3.1-flash-lite.

Fixes #89390

* test(google): cover Gemini flash lite catalog row

---------

Co-authored-by: Peter Steinberger <steipete@gmail.com>

extensions/google/provider-catalog.test.ts

@@ -11,8 +11,13 @@ describe("google provider catalog", () => {
     expect(provider.api).toBe("google-vertex");
     expect(provider.baseUrl).toBe("https://{location}-aiplatform.googleapis.com");
     expect(provider.models.map((model) => model.id)).toEqual(
-      expect.arrayContaining(["gemini-2.5-pro", "gemini-3.1-pro-preview"]),
+      expect.arrayContaining(["gemini-2.5-pro", "gemini-3.1-pro-preview", "gemini-3.1-flash-lite"]),
     );
+    expect(provider.models.find((model) => model.id === "gemini-3.1-flash-lite")).toMatchObject({
+      contextWindow: 1_048_576,
+      maxTokens: 65_536,
+      reasoning: true,
+    });
   });
 
   it("keeps Google AI Studio and Vertex model ids aligned", () => {

extensions/google/provider-catalog.ts

@@ -43,6 +43,15 @@ const GOOGLE_GEMINI_TEXT_MODELS: ModelDefinitionConfig[] = [
     contextWindow: 1_048_576,
     maxTokens: 65_536,
   },
+  {
+    id: "gemini-3.1-flash-lite",
+    name: "Gemini 3.1 Flash Lite",
+    reasoning: true,
+    input: ["text", "image"],
+    cost: GOOGLE_GEMINI_COST,
+    contextWindow: 1_048_576,
+    maxTokens: 65_536,
+  },
   {
     id: "gemini-3-flash-preview",
     name: "Gemini 3 Flash Preview",