feat: add gemini 2.5 flash image support

backend/internal/pkg/geminicli/models_test.go

@@ -0,0 +1,23 @@
+package geminicli
+
+import "testing"
+
+func TestDefaultModels_ContainsImageModels(t *testing.T) {
+	t.Parallel()
+
+	byID := make(map[string]Model, len(DefaultModels))
+	for _, model := range DefaultModels {
+		byID[model.ID] = model
+	}
+
+	required := []string{
+		"gemini-2.5-flash-image",
+		"gemini-3.1-flash-image",
+	}
+
+	for _, id := range required {
+		if _, ok := byID[id]; !ok {
+			t.Fatalf("expected curated Gemini model %q to exist", id)
+		}
+	}
+}