Add IPFS node to L2 for federated content storage

- Add IPFS container to docker-compose
- Add ipfshttpclient dependency
- Add ipfs_client.py module for IPFS operations
- Add ipfs_cid field to Asset model and database schema
- Pin content on L2 IPFS when assets are published/registered

L2 now stores content on its own IPFS node, enabling
federation - content remains available even if L1 goes down.

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

ipfs_client.py

@@ -0,0 +1,117 @@
+# art-activity-pub/ipfs_client.py
+"""
+IPFS client for Art DAG L2 server.
+
+Provides functions to fetch and pin content from IPFS.
+L2 uses IPFS to retrieve content from the federated network.
+"""
+
+import logging
+import os
+from typing import Optional
+
+import ipfshttpclient
+
+logger = logging.getLogger(__name__)
+
+# IPFS API multiaddr - default to local, docker uses /dns/ipfs/tcp/5001
+IPFS_API = os.getenv("IPFS_API", "/ip4/127.0.0.1/tcp/5001")
+
+# Connection timeout in seconds
+IPFS_TIMEOUT = int(os.getenv("IPFS_TIMEOUT", "60"))
+
+
+def get_client():
+    """Get an IPFS client connection."""
+    return ipfshttpclient.connect(IPFS_API, timeout=IPFS_TIMEOUT)
+
+
+def get_bytes(cid: str) -> Optional[bytes]:
+    """
+    Retrieve content from IPFS by CID.
+
+    Args:
+        cid: IPFS CID to retrieve
+
+    Returns:
+        Content as bytes or None on failure
+    """
+    try:
+        with get_client() as client:
+            data = client.cat(cid)
+            logger.info(f"Retrieved from IPFS: {cid} ({len(data)} bytes)")
+            return data
+    except Exception as e:
+        logger.error(f"Failed to get from IPFS: {e}")
+        return None
+
+
+def pin(cid: str) -> bool:
+    """
+    Pin a CID on this node.
+
+    Args:
+        cid: IPFS CID to pin
+
+    Returns:
+        True on success, False on failure
+    """
+    try:
+        with get_client() as client:
+            client.pin.add(cid)
+            logger.info(f"Pinned on IPFS: {cid}")
+            return True
+    except Exception as e:
+        logger.error(f"Failed to pin on IPFS: {e}")
+        return False
+
+
+def unpin(cid: str) -> bool:
+    """
+    Unpin a CID from this node.
+
+    Args:
+        cid: IPFS CID to unpin
+
+    Returns:
+        True on success, False on failure
+    """
+    try:
+        with get_client() as client:
+            client.pin.rm(cid)
+            logger.info(f"Unpinned from IPFS: {cid}")
+            return True
+    except Exception as e:
+        logger.error(f"Failed to unpin from IPFS: {e}")
+        return False
+
+
+def is_available() -> bool:
+    """
+    Check if IPFS daemon is available.
+
+    Returns:
+        True if IPFS is available, False otherwise
+    """
+    try:
+        with get_client() as client:
+            client.id()
+            return True
+    except Exception:
+        return False
+
+
+def get_node_id() -> Optional[str]:
+    """
+    Get this IPFS node's peer ID.
+
+    Returns:
+        Peer ID string or None on failure
+    """
+    try:
+        with get_client() as client:
+            info = client.id()
+            return info.get("ID")
+    except Exception as e:
+        logger.error(f"Failed to get node ID: {e}")
+        return None