Use default color in Loader component for CSS variable (#12844)

Fixes a regression introduced by
https://github.com/twentyhq/twenty/pull/11639

cc @AMoreaux 

## Before

![CleanShot 2025-06-24 at 17 20
21@2x](https://github.com/user-attachments/assets/8360da38-98b7-42a0-91b8-15caa5dde802)

## After

![CleanShot 2025-06-24 at 17 18
21@2x](https://github.com/user-attachments/assets/9953ec11-f22c-49ea-9023-fe42e79761b5)



https://github.com/user-attachments/assets/875c6c7e-3fc3-44bf-bb17-69ca362c1145

packages/twenty-ui/src/feedback/loader/components/Loader.tsx

@@ -15,7 +15,9 @@ const StyledLoaderContainer = styled.div<{
   border-radius: ${({ theme }) => theme.border.radius.pill};
   border: 1px solid
     ${({ color, theme }) =>
-      color ? theme.tag.text[color] : `var(--tw-button-color)`};
+      color
+        ? theme.tag.text[color]
+        : `var(--tw-button-color, ${theme.font.color.tertiary})`};
   overflow: hidden;
 `;
 
@@ -23,7 +25,9 @@ const StyledLoader = styled(motion.div)<{
   color?: ThemeColor;
 }>`
   background-color: ${({ color, theme }) =>
-    color ? theme.tag.text[color] : `var(--tw-button-color)`};
+    color
+      ? theme.tag.text[color]
+      : `var(--tw-button-color, ${theme.font.color.tertiary})`};
   border-radius: ${({ theme }) => theme.border.radius.pill};
   height: 8px;
   width: 8px;