Complete React 19 upgrade with dependency and type fixes

[Copilot]

Dependabot only upgraded react-dom to v19, leaving react on v18, causing version mismatch failures. React 19 requires all packages in the ecosystem to be upgraded together.

Package upgrades

• react: 18.3.1 → 19.2.0
• @types/react: 18.3.12 → 19.2.2
• @fluentui/react: 8.112.5 → 8.125.0
• @fluentui/react-components: 9.56.2 → 9.72.4
• @react-spring/web: 9.7.5 → 10.0.3

TypeScript fixes for React 19

React 19 removes the global JSX namespace. Changed explicit return types to rely on inference:

// Before (React 18)
export function Component(): JSX.Element {
  return <div>...</div>;
}

// After (React 19)
export function Component() {
  return <div>...</div>;
}

Updated useRef typing syntax:

// Before
const ref: RefObject<HTMLDivElement> = useRef(null);

// After
const ref = useRef<HTMLDivElement>(null);

Configuration

Added legacy-peer-deps=true to .npmrc for react-helmet-async which doesn't declare React 19 support but functions correctly with it.

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