fix: redirect root / to /platform/ for better UX

Users hitting the root URL now get redirected to the SaaS app instead
of seeing Logto's unknown-session page.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -147,6 +147,13 @@ services:
       - traefik.http.routers.saas.entrypoints=websecure
       - traefik.http.routers.saas.tls=true
       - traefik.http.services.saas.loadbalancer.server.port=8080
+      - traefik.http.routers.root-redirect.rule=Path(`/`)
+      - traefik.http.routers.root-redirect.entrypoints=websecure
+      - traefik.http.routers.root-redirect.tls=true
+      - traefik.http.routers.root-redirect.middlewares=root-to-platform
+      - traefik.http.routers.root-redirect.service=saas
+      - traefik.http.middlewares.root-to-platform.redirectregex.regex=^/$
+      - traefik.http.middlewares.root-to-platform.redirectregex.replacement=/platform/
     networks:
       - cameleer