feat: initial recipes repo with identity-cat

- Recipe schema using artdag primitives (SOURCE, EFFECT)
- identity-cat: applies identity effect to cat image
- Test verifying identity property: output_hash == input_hash
- Demonstrates content-addressed DAG execution

Owner: @giles@artdag.rose-ash.com

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

README.md

@@ -0,0 +1,30 @@
+# Art DAG Recipes
+
+Recipes that transform assets using effects from [art-dag](https://github.com/gilesbradshaw/art-dag).
+
+## Structure
+
+```
+recipes/
+└── identity-cat/
+    ├── recipe.yaml    # DAG definition
+    └── README.md      # Description
+```
+
+## Registry References
+
+Recipes reference assets and effects by content hash from:
+- **Assets**: https://github.com/gilesbradshaw/art-dag/blob/main/registry/registry.json
+- **Effects**: https://github.com/gilesbradshaw/art-dag/tree/main/effects
+
+## Recipe Schema
+
+A recipe is a DAG with:
+- `name`: Unique recipe identifier
+- `inputs`: Assets referenced by content_hash
+- `nodes`: DAG nodes using primitives (SOURCE, TRANSFORM, etc.) and effects
+- `output`: Expected output hash (for verification)
+
+## Owner
+
+Recipes owned by `@giles@artdag.rose-ash.com`