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>

db.py

@@ -52,6 +52,7 @@ CREATE TABLE IF NOT EXISTS users (
 CREATE TABLE IF NOT EXISTS assets (
     name VARCHAR(255) PRIMARY KEY,
     content_hash VARCHAR(128) NOT NULL,
+    ipfs_cid VARCHAR(128),
     asset_type VARCHAR(50) NOT NULL,
     tags JSONB DEFAULT '[]'::jsonb,
     metadata JSONB DEFAULT '{}'::jsonb,
@@ -248,12 +249,13 @@ async def create_asset(asset: dict) -> dict:
     """Create a new asset."""
     async with get_connection() as conn:
         row = await conn.fetchrow(
-            """INSERT INTO assets (name, content_hash, asset_type, tags, metadata,
+            """INSERT INTO assets (name, content_hash, ipfs_cid, asset_type, tags, metadata,
                                    url, provenance, description, origin, owner, created_at)
-               VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11)
+               VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12)
                RETURNING *""",
             asset["name"],
             asset["content_hash"],
+            asset.get("ipfs_cid"),
             asset["asset_type"],
             json.dumps(asset.get("tags", [])),
             json.dumps(asset.get("metadata", {})),