Route storefront marketplace under /storefront

Replace the legacy /explore marketplace route with /storefront across the
storefront app and production routing.

- move the marketplace index page to the storefront root route
- move company and vehicle detail pages from /explore/* to /* internally
- update marketplace links, renter dashboard links, saved company links, and
  header navigation to target /storefront
- remove remaining explore route references and wording from storefront code
- configure production Traefik to route /storefront and strip the prefix before
  forwarding to the storefront service
- set the storefront production asset prefix to /storefront so Next chunks load
  from /storefront/_next instead of the shared root /_next path
- redirect locale entry paths such as /storefront/fr back to /storefront while
  persisting the selected language cookie
- update middleware tests for the locale redirect and adjusted redirect mock

Verification:
- npm run test --workspace @rentaldrivego/storefront
- npm run build --workspace @rentaldrivego/storefront

docker-compose.production.yml

@@ -215,14 +215,15 @@ services:
     restart: unless-stopped
     labels:
       - traefik.enable=true
-      - traefik.http.routers.storefront.rule=(Host(`${PUBLIC_SITE_DOMAIN}`) || Host(`www.${PUBLIC_SITE_DOMAIN}`)) && PathPrefix(`/explore`, `/renter`, `/sign-in`, `/footer`, `/app-privacy`, `/app-tc`, `/company-workspace`)
+      - traefik.http.routers.storefront.rule=(Host(`${PUBLIC_SITE_DOMAIN}`) || Host(`www.${PUBLIC_SITE_DOMAIN}`)) && PathPrefix(`/storefront`, `/renter`, `/sign-in`, `/footer`, `/app-privacy`, `/app-tc`, `/company-workspace`)
       - traefik.http.routers.storefront.entrypoints=websecure
       - traefik.http.routers.storefront.tls=true
       - traefik.http.routers.storefront.tls.certresolver=letsencrypt
       - traefik.http.routers.storefront.service=storefront-svc
       - traefik.http.routers.storefront.priority=20
       - traefik.http.services.storefront-svc.loadbalancer.server.port=3004
-      - traefik.http.routers.storefront.middlewares=rdg-security-headers@docker
+      - traefik.http.middlewares.storefront-strip-prefix.stripprefix.prefixes=/storefront
+      - traefik.http.routers.storefront.middlewares=storefront-strip-prefix,rdg-security-headers@docker
 
   dashboard:
     <<: *node-runtime-hardening