fix(web): wire up next-intl i18n — install dep, add locale middleware, wrap next config

The i18n architecture (config, routing, translation files, locale pages) was
already built but non-functional due to three missing pieces:
1. next-intl not listed in package.json
2. middleware.ts not using createMiddleware from next-intl/middleware
3. next.config.js not wrapped with createNextIntlPlugin

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/package.json

@@ -19,6 +19,7 @@
     "lucide-react": "^1.7.0",
     "mapbox-gl": "^3.21.0",
     "next": "^14.2.0",
+    "next-intl": "^4.9.0",
     "react": "^18.3.0",
     "react-dom": "^18.3.0",
     "react-hook-form": "^7.72.1",