Fix: Frontend build errors in ManageProjects and buttonGroup components

Fixed two build errors preventing the frontend Docker image from building:

1. Removed duplicate 'display' key in loadingStyle object (ManageProjects.jsx)
   - The loadingStyle object had both "display": "none" and "display": "flex"
   - Kept "display": "flex" which is correct for the loading overlay
   - Introduced in commit 3a25f7f by JamesNg on 2025-01-29

2. Replaced non-existent StyledButton import with MUI Button (buttonGroup.jsx)
   - Component was importing StyledButton from ProjectForm.jsx
   - StyledButton export was removed in commit 8e9ac7b by Kaipher on 2025-10-06
   - Component was created in commit cf194d2 by JamesNg on 2025-09-29
   - Updated to use standard MUI Button component with matching styles

Build errors resolved:
- "Duplicate key 'display' in object literal"
- "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>
 );

client/src/pages/ManageProjects.jsx

@@ -17,7 +17,6 @@ const PAGES = Object.freeze({
 
 // Added styles for MUI components
 const loadingStyle = {
-  "display": "none",
   "position": "absolute",
   "display": "flex",
   "flexDirection": "row",