Two new services on LXC 125's docker stack:
- seafile-md-server (Pro extended metadata, internal-only on :8084)
- thumbnail-server (Pro accelerated thumbnails, bound to .185:8081)
Caddy now routes /thumbnail/* to the thumbnail-server; everything else stays
on the main seafile container. End-to-end smoke verified: routing works,
per-request permission checks via INNER_SEAHUB_SERVICE_URL=http://seafile
correctly return 403 for cross-user thumbnail requests.
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