[WV-4833] Upgrade to Mui 7, or to the latest version MUI 9 (from MUI 5)

[pravingv]

What github.com/wevote/WebApp/issues does this fix?

WV-4833 Upgrade to Mui 7, or to the latest version MUI 9 (from MUI 5)

Changes included this pull request?

Foundation & Package Alignment (package.json):

• Upgraded @mui/material, @mui/icons-material, @mui/lab, and @mui/styled-engine-sc to ^9.0.0.
• Upgraded react and react-dom to ~18.3.1.
• Upgraded styled-components to ~6.1.8, @stripe/react-stripe-js to ^2.5.0, react-toastify to ^10.0.0, and removed obsolete react-hot-loader.
• Added explicit npm overrides for "@mui/system": "^9.0.0" and "@mui/styled-engine": "^9.0.0" to ensure internal dependency synchronization.

Core Engine & Multi-Engine Theme Alignment (src/index.jsx, src/App.jsx):

• src/index.jsx: Replaced deprecated ReactDOM.render with React 18 createRoot(container).render(...).
• src/App.jsx: Implemented Proposal 1 (App-Level Multi-Engine Theme Provider Alignment) by nesting (@mui/styles) and (styled-components) under @mui/material/styles's . This resolved theme.spacing and theme.breakpoints crashes across all legacy and modern styling engines without touching individual components.

Icon Exports & Concurrent Effect Lifecycle Cleanup:

• Replaced deprecated icon exports across 8 component files (MailOutline -> Mail, DeleteOutline -> DeleteOutlined, PersonOutline -> Person, ChatBubbleOutline -> Comment).
• Fixed React 18 useEffect cleanup returns in DisplayWhileRetrievingBallot.jsx and ReviewAppModal.jsx: changed return null / return <></> to return undefined to eliminate TypeError: destroy is not a function.

Codebase-Wide Styled-Components Syntax Standardization (96 Files):

• Converted all 96 styled-components files from unsupported 2nd-argument options syntax (styled('tag', { shouldForwardProp })) to .withConfig({ shouldForwardProp }).
• Resolved DOM attribute casing and typos: corrected styleid to standard id in BallotTitleHeaderStyles.jsx, and filtered fetchpriority in CampaignCardStyles.jsx while preserving lowercase fetchpriority="high" in JSX per user directive.
• Filtered custom props across components (showAsLink, hideCardMargins, animate, selected, primary, secondary, size, scrolledDown, padTop, padBottom, desktopMode, leftAlign).

MUI Layout & Form Component API Modernization:

• Refactored top-level layout props (justifyContent, display, gap, alignItems) into the sx prop on across CardForListBody.jsx, CardForListBodySkeleton.jsx, OrganizationModal.jsx, and PoliticianDetailsEndorsementsSkeleton.jsx.
• Migrated legacy InputProps on to MUI v9 slotProps={{ input: { ... } }} in VoterPhoneVerificationEntry.jsx and VoterEmailAddressEntry.jsx.
• Removed invalid icon prop from in TextBox.jsx.
• Migrated legacy <Dialog ModalProps={{ disableScrollLock: true }}> to standard top-level prop in ShareModal.jsx.
• Removed unused ContentProps from wrapping in SnackNotifier.jsx.

React PropTypes & Modal State Hardening (35 Modal Files):

• Audited all modal and dialog components across src/js/ and cast the required open prop on and to Boolean() (open={Boolean(show)}) across 35 modal files to prevent React PropTypes undefined warnings.