Show CID for asset uploads

- Display IPFS CID after upload
- Show recipe syntax with :cid

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

artdag.py

@@ -519,7 +519,7 @@ def import_file(filepath):
 @cli.command()
 @click.argument("filepath", type=click.Path(exists=True))
 def upload(filepath):
-    """Upload a file to cache (works with remote servers). Requires login."""
+    """Upload a file to cache and IPFS. Requires login."""
     # Check auth
     token_data = load_token()
     if not token_data.get("access_token"):
@@ -536,8 +536,11 @@ def upload(filepath):
                 sys.exit(1)
             resp.raise_for_status()
             result = resp.json()
-        click.echo(f"Uploaded: {result['content_hash']}")
+        click.echo(f"CID: {result['cid']}")
         click.echo(f"Size: {result['size']} bytes")
+        click.echo()
+        click.echo("Use in recipes:")
+        click.echo(f'  (asset my-asset :cid "{result["cid"]}")')
     except requests.RequestException as e:
         click.echo(f"Upload failed: {e}", err=True)
         sys.exit(1)