Consume coop fragments for unified navigation

Add middleware to fetch nav-tree, auth-menu, and cart-mini fragments
from coop apps. Update base.html to render coop nav with fallback.
Add internal URL env vars for Docker networking.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -73,6 +73,10 @@ services:
       # IPFS_API multiaddr - used for all IPFS operations (add, cat, pin)
       - IPFS_API=/dns/ipfs/tcp/5001
       - CACHE_DIR=/data/cache
+      # Coop app internal URLs for fragment composition
+      - INTERNAL_URL_BLOG=http://blog:8000
+      - INTERNAL_URL_CART=http://cart:8000
+      - INTERNAL_URL_ACCOUNT=http://account:8000
       # DATABASE_URL, ADMIN_TOKEN, ARTDAG_CLUSTER_KEY,
       # L2_SERVER, L2_DOMAIN, IPFS_GATEWAY_URL from .env file
     healthcheck: