chore(frontend): Upgrade MUI v5 → v7

- @mui/material: 5.18.0 → 7.3.3
- @mui/icons-material: 5.18.0 → 7.3.3
- @mui/material-nextjs: 7.3.2 → 7.3.3

Server working correctly with MUI v7:
- All pages compile successfully
- HTTP 200 on all routes
- No MUI-related errors

maternal-web/package.json

@@ -18,9 +18,9 @@
     "@emotion/react": "^11.14.0",
     "@emotion/styled": "^11.14.1",
     "@hookform/resolvers": "^5.2.2",
-    "@mui/icons-material": "^5.18.0",
-    "@mui/material": "^5.18.0",
-    "@mui/material-nextjs": "^7.3.2",
+    "@mui/icons-material": "^7.3.3",
+    "@mui/material": "^7.3.3",
+    "@mui/material-nextjs": "^7.3.3",
     "@reduxjs/toolkit": "^2.9.0",
     "@simplewebauthn/browser": "^13.2.0",
     "@tanstack/react-query": "^5.90.2",