fix(frontend): don't preselect core brain (#2239)

# Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

frontend/lib/components/AddBrainModal/components/BrainTypeSelectionStep/BrainTypeSelectionStep.tsx

@@ -13,7 +13,7 @@ import { useBrainCreationContext } from "../../brainCreation-provider";
 import { useBrainCreationSteps } from "../../hooks/useBrainCreationSteps";
 
 export const BrainTypeSelectionStep = (): JSX.Element => {
-  const [selectedIndex, setSelectedIndex] = useState<number>(0);
+  const [selectedIndex, setSelectedIndex] = useState<number>(-1);
   const [customBrainsCatalogueOpened, setCustomBrainsCatalogueOpened] =
     useState<boolean>(false);
   const [customBrains, setCustomBrains] = useState<IntegrationBrains[]>([]);

frontend/lib/components/AddBrainModal/components/CreateBrainStep/CreateBrainStep.tsx

@@ -48,7 +48,7 @@ export const CreateBrainStep = (): JSX.Element => {
           onClick={previous}
         />
         <QuivrButton
-          label="Create brain"
+          label="Create"
           color="primary"
           iconName="add"
           onClick={feed}