deps: react-migration-to-v19

[Zaimwa9]

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• I have filled in the "Changes" section below.
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Changes

Upgrades the frontend from React 16 to React 19, along with all incompatible dependencies.

React 19 migration

• Updated react and react-dom from 16.14.0 to 19.x
• Updated @types/react and @types/react-dom to 19.x
• Configured Babel with "runtime": "automatic" for the new JSX transform
• Removed @babel/transform-react-inline-elements (incompatible with React 19)
• Updated tsconfig.json and tsconfig.jest.json to use "jsx": "react-jsx"
• Deleted legacy common/Component.js (used React.createClass, removed in React 19)
• Removed string refs (ref='wrappedComponent') from ConfigProvider and withSegmentOverrides

Dependency replacements

• @material-ui/core → native implementations: Material UI v4 is incompatible with React 19
  • AccordionCard: replaced and with a custom height-animated accordion using useRef/useEffect
  • ChipInput: replaced material-ui-chip-input with a custom chip input component
  • SegmentSelect: removed @material-ui/core/Select type import, replaced with plain types
• react-sortable-hoc → @dnd-kit/core + @dnd-kit/sortable: react-sortable-hoc relies on deprecated findDOMNode, incompatible with
  React 19. Migrated SegmentOverrides to use @dnd-kit with DndContext, SortableContext, and useSortable
• react-select 2.x → 5.x: Updated for React 19 compatibility
• react-click-outside: Removed (unused/incompatible)
• react-window, react-window-infinite-loader, react-virtualized-auto-sizer: Removed (unused)
• reactstrap: Updated from 9.0.1 to 9.2.3

react-tooltip v4 → v5 (performance fix)

• Upgraded react-tooltip from 4.5.1 to 5.30.0 to fix severe UI lag when horizontally resizing the browser on pages with many
  feature rows
• v4 created a separate DOM element per tooltip instance, each registering global resize and scroll event listeners — hundreds of
  listeners firing synchronously per resize frame
• v5 uses floating-ui: tooltips are only materialised on hover, eliminating idle listeners
• Migrated Tooltip.tsx to v5 API (data-tooltip-id/data-tooltip-html replacing data-for/data-tip)
• Removed the TooltipPortal helper (v5 handles portalling internally)
• Replaced Utils.GUID() with React useId() for stable tooltip IDs
• Updated _tooltips.scss selectors from .__react_component_tooltip to .react-tooltip
• Updated tooltip usage in Modal.tsx, ModalConfirm.tsx, and SegmentOverrides.js

Other fixes

• Fixed AccordionCard chevron showing oversized focus ring (replaced with )

How did you test this code?

Please describe.

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Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-api-test:pr-6764	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api:pr-6764	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-e2e:pr-6764	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith:pr-6764	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-6764	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-frontend:pr-6764	Finished ✅	Results ✅