Fix: Replace non-existent StyledButton with MUI Button component

The buttonGroup component was importing StyledButton from ProjectForm.jsx, but this export no longer exists in that file. This caused a build error during the Vite build process.

Replaced StyledButton with the standard MUI Button component and updated the styling to match the patterns used in ProjectForm.jsx (width: 150px, cursor: pointer).

This fixes the build error:
"StyledButton" is not exported by "src/components/ProjectForm.jsx"

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

Author: 3 people

client/src/components/manageProjects/editPMs/buttonGroup.jsx

@@ -1,27 +1,24 @@
-import { CircularProgress, Grid } from "@mui/material";
-import { StyledButton } from '../../ProjectForm';
+import { CircularProgress, Grid, Button } from "@mui/material";
 
 const ButtonGroup = ({ btnName1, btnName2, callBackFn1, callBackFn2, isLoading }) => (
   <Grid container justifyContent="space-evenly" sx={{ my: 3 }}>
     <Grid item xs="auto">
-      <StyledButton
-        sx="large"
-        cursor="pointer"
+      <Button
+        sx={{ width: '150px', cursor: 'pointer' }}
         variant="contained"
         onClick={(btn) => callBackFn1(btn)}
       >
         {isLoading ? <CircularProgress /> : `${btnName1}`}
-      </StyledButton>
+      </Button>
     </Grid>
     <Grid item xs="auto">
-      <StyledButton
-        sx="large"
-        cursor="pointer"
+      <Button
+        sx={{ width: '150px', cursor: 'pointer' }}
         variant="contained"
         onClick={callBackFn2}
       >
         {btnName2}
-      </StyledButton>
+      </Button>
     </Grid>
   </Grid>
 );