feat: Traefik router labels for prod deploy

Add traefik.enable + Host/entrypoints/tls/certresolver/service labels to the
prod override, driven by MANGA_API_HOST / PROXY_NETWORK / TRAEFIK_ENTRYPOINT /
TRAEFIK_CERTRESOLVER env vars (documented in .env.example).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.prod.yml

@@ -1,19 +1,31 @@
-# Production override: attach to an existing external reverse-proxy Docker
-# network instead of publishing a host port. The proxy routes
-# manga-api.<domain> -> manga-api:8080 over the shared network.
+# Production override: join an existing Traefik network and let Traefik route
+# manga-api.<domain> -> this service with TLS. No host port published.
 #
-#   docker compose -f docker-compose.yml -f docker-compose.prod.yml up -d
+#   docker compose -f docker-compose.yml -f docker-compose.prod.yml up -d --build
 #
-# The network must already exist (created by your proxy stack):
+# Set in .env:
+#   MANGA_API_HOST=manga-api.example.com   # your subdomain (required)
+#   PROXY_NETWORK=proxy                     # Traefik's network name, if not "proxy"
+#   TRAEFIK_ENTRYPOINT=websecure            # your HTTPS entrypoint name
+#   TRAEFIK_CERTRESOLVER=le                 # your ACME/cert resolver name
+#
+# The network must already exist and Traefik must watch it:
 #   docker network create proxy   # if it doesn't yet
-# Override the name with PROXY_NETWORK in .env if yours differs.
 
 services:
   manga-api:
-    # Drop the loopback port publish; traffic comes over the proxy network.
+    # Traffic arrives over the Traefik network, not a published port.
     ports: !reset []
     networks:
       - proxy
+    labels:
+      - "traefik.enable=true"
+      - "traefik.docker.network=${PROXY_NETWORK:-proxy}"
+      - "traefik.http.routers.mangabm.rule=Host(`${MANGA_API_HOST:?set MANGA_API_HOST in .env}`)"
+      - "traefik.http.routers.mangabm.entrypoints=${TRAEFIK_ENTRYPOINT:-websecure}"
+      - "traefik.http.routers.mangabm.tls=true"
+      - "traefik.http.routers.mangabm.tls.certresolver=${TRAEFIK_CERTRESOLVER:-le}"
+      - "traefik.http.services.mangabm.loadbalancer.server.port=8080"
 
 networks:
   proxy: