Add format_date helper to handle datetime objects in templates

The db now returns datetime objects instead of strings in some cases.
Added format_date() helper function that handles both datetime and string
values, and replaced all [:10] date slicing with calls to this helper.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker-compose.yml

@@ -40,9 +40,11 @@ services:
       - ARTDAG_DATA=/data/l2
       - DATABASE_URL=postgresql://artdag:${POSTGRES_PASSWORD:-artdag}@postgres:5432/artdag
       - IPFS_API=/dns/ipfs/tcp/5001
+      - ANCHOR_BACKUP_DIR=/data/anchors
       # ARTDAG_DOMAIN, ARTDAG_USER, JWT_SECRET from .env file
     volumes:
       - l2_data:/data/l2  # Still needed for RSA keys
+      - anchor_backup:/data/anchors  # Persistent anchor proofs (survives DB wipes)
     networks:
       - internal
       - externalnet
@@ -58,6 +60,7 @@ volumes:
   l2_data:
   postgres_data:
   ipfs_data:
+  anchor_backup:  # Persistent - don't delete when resetting DB
 
 networks:
   internal: