Lovable i18n: translate TanStack Start apps

Add multilingual support to this Lovable app with Lovalingo.

npm install @lovalingo/lovalingo

Detect the app stack first.

If this project uses TanStack Start:
- preserve TanStack Start routing and server rendering
- mount the Lovalingo runtime from @lovalingo/lovalingo/core in client code
- add locale URLs for /en, /es, /fr, /nl
- make /:locale/* routes return HTTP 200
- render the correct html[lang], canonical, hreflang, title, meta description, OG, and Twitter tags on the server
- add the Lovalingo language switcher
- keep /.well-known/lovalingo.json, /robots.txt, and /sitemap.xml unprefixed

If this project is a legacy React/Vite Lovable app:
- use LovalingoProvider at the root
- enable routing="path"
- add the Lovalingo language switcher

import { LovalingoProvider } from '@lovalingo/lovalingo/core';

<LovalingoProvider
  publicAnonKey="YOUR_PUBLIC_KEY"
  defaultLocale="en"
  locales={["fr", "es", "de", "it"]}
  routing="path"
>
  <App />
</LovalingoProvider>

For legacy React/Vite apps, add a language switcher anywhere in the UI:

import { LanguageSwitcher } from '@lovalingo/lovalingo/core';
<LanguageSwitcher />

After setup, verify:
- /es returns 200
- the switcher appears
- html[lang], canonical, hreflang, and translated metadata are present in the initial HTML