Update the frontend to React 19 and enable the React Compiler #740

Description

Upgrade the frontend to React 19 and enable the React Compiler. React 19 brings automatic memoization via the Compiler and better runtime performance. This upgrade removes boilerplate and prepares the codebase for future React 19 features.

Acceptance criteria

• React and React DOM upgraded from 18.3.1 to 19.2.7
• @types/react and @types/react-dom upgraded to ^19.0.0
• babel-plugin-react-compiler added and enabled in vite.config.ts
• All Blueprint.js dependencies upgraded to versions that officially support React 19 (18 || 19):
  • @blueprintjs/core: 6.11.3 → 6.16.0
  • @blueprintjs/icons: 6.8.0 → 6.11.0
  • @blueprintjs/select: 6.1.8 → 6.3.0
• Manual useMemo and useCallback removed — React Compiler handles memoization automatically
• <Context.Provider> simplified to <Context> using React 19 syntax
• tsc --noEmit passes without errors
• vite build succeeds
• ESLint shows no new errors (pre-existing warnings are unchanged)
• npm install succeeds without --legacy-peer-deps

Implementation references

• https://react.dev/blog/2024/12/05/react-19
• https://react.dev/learn/react-compiler
• https://github.com/palantir/blueprint/releases

Scope

• frontend/package.json
• frontend/vite.config.ts
• frontend/src/common/ThemeManager.tsx
• frontend/src/context/ProxyStateContext.tsx

Originally posted by @kamalovk in #732 (reply in thread)