Add testing infrastructure and refactor DAG transformation

Testing setup:
- Add pyproject.toml with mypy and pytest configuration
- Add requirements-dev.txt for development dependencies
- Create tests/ directory with test fixtures
- Add 17 unit tests for DAG transformation pipeline

Type annotations:
- Add app/types.py with TypedDict definitions for node configs
- Add typed helper functions: transform_node, build_input_name_mapping,
  bind_inputs, prepare_dag_for_execution
- Refactor run_recipe to use the new typed helpers

Regression tests for today's bugs:
- test_effect_cid_key_not_effect_hash: Verifies CID uses 'cid' key
- test_source_cid_binding_persists: Verifies bound CIDs in final DAG

Run tests with: pytest tests/ -v

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

pyproject.toml

@@ -0,0 +1,51 @@
+[project]
+name = "art-celery"
+version = "0.1.0"
+description = "Art DAG L1 Server and Celery Workers"
+requires-python = ">=3.11"
+
+[tool.mypy]
+python_version = "3.11"
+warn_return_any = true
+warn_unused_ignores = true
+disallow_untyped_defs = true
+disallow_incomplete_defs = true
+check_untyped_defs = true
+strict_optional = true
+no_implicit_optional = true
+
+# Start strict on new code, gradually enable for existing
+files = [
+    "app/types.py",
+    "app/routers/recipes.py",
+    "tests/",
+]
+
+# Ignore missing imports for third-party packages without stubs
+[[tool.mypy.overrides]]
+module = [
+    "celery.*",
+    "redis.*",
+    "artdag.*",
+    "artdag_common.*",
+    "ipfs_client.*",
+]
+ignore_missing_imports = true
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+python_files = ["test_*.py"]
+python_functions = ["test_*"]
+asyncio_mode = "auto"
+addopts = "-v --tb=short"
+filterwarnings = [
+    "ignore::DeprecationWarning",
+]
+
+[tool.ruff]
+line-length = 100
+target-version = "py311"
+
+[tool.ruff.lint]
+select = ["E", "F", "I", "UP"]
+ignore = ["E501"]  # Line length handled separately