fix: add strip-prefix back to server-ui route

Server-ui injects BASE_PATH=/server/ into <base href>. Without strip-prefix,
Traefik forwards /server/ path AND server-ui adds /server/ again = double prefix.
Strip /server before forwarding so server-ui sees / and produces correct <base href="/server/">.

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

docker-compose.yml

@@ -203,6 +203,8 @@ services:
       - traefik.http.routers.server-ui.rule=PathPrefix(`/server`)
       - traefik.http.routers.server-ui.entrypoints=websecure
       - traefik.http.routers.server-ui.tls=true
+      - traefik.http.routers.server-ui.middlewares=server-ui-strip
+      - traefik.http.middlewares.server-ui-strip.stripprefix.prefixes=/server
       - traefik.http.routers.server-ui.service=server-ui
       - traefik.http.services.server-ui.loadbalancer.server.port=80
     networks: