chore(deps): upgrade React 18.3 -> 19.2.7

react / react-dom 18.3.1 -> 19.2.7; @types/react 18.3.31 -> 19.2.17;
@types/react-dom 18.3.7 -> 19.2.3 (latest stable 19.2.x).

Only breaking change hitting our code: React 19 removed the no-arg useRef<T>()
overload. AppShell's logoutTimer -> useRef<T | undefined>(undefined) — the same
transform the official `types-react-codemod preset-19` (useRef-required-initial)
applies. No other preset-19 transforms were relevant (already on createRoot; no
ReactDOM.render, string refs, propTypes/defaultProps on function components).

No Next.js / RSC in this project (it's a Vite SPA served by Fastify), so those
React 19 concerns don't apply here. MUI v7, framer-motion 12, TanStack Query 5,
react-router-dom 6 and react-quill-new all installed cleanly against React 19
(no peer-dependency conflicts).

Gates: tsc 0 | build 0 | vitest 247/247 | eslint 0 errors.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package.json

@@ -66,8 +66,8 @@
     "prisma": "^6.19.2",
     "puppeteer": "^24.40.0",
     "qrcode": "^1.5.4",
-    "react": "^18.3.1",
-    "react-dom": "^18.3.1",
+    "react": "^19.2.7",
+    "react-dom": "^19.2.7",
     "react-quill-new": "^3.8.3",
     "react-router-dom": "^6.30.3",
     "zod": "^4.3.6"
@@ -82,8 +82,8 @@
     "@types/node-cron": "^3.0.11",
     "@types/nodemailer": "^7.0.11",
     "@types/qrcode": "^1.5.6",
-    "@types/react": "^18.3.31",
-    "@types/react-dom": "^18.3.7",
+    "@types/react": "^19.2.17",
+    "@types/react-dom": "^19.2.3",
     "@types/supertest": "^7.2.0",
     "@vitejs/plugin-react": "^6.0.1",
     "concurrently": "^9.2.1",