test: add integration tests for all modules

- Add pytest-asyncio dev dependency and configure asyncio_mode=auto
- Add filterwarnings to suppress third-party PydanticDeprecatedSince20
- Add conftest.py with shared fixtures (project_dir, write_config, etc.)
- Add test_config.py: YAML loading, target type inference, model resolution
- Add test_graph.py: DAG construction, cycle detection, build ordering
- Add test_state.py: hash functions, state persistence, dirty checking
- Add test_builder.py: full build pipeline with FakeProvider, incremental
  builds, selective builds, error isolation, dependency cascading
- Add test_providers.py: ImageProvider and TextProvider with mocked clients
- Add test_cli.py: build/clean/graph commands via typer CliRunner
- All 94 tests pass with 0 basedpyright warnings

tests/conftest.py

@@ -0,0 +1,79 @@
+"""Shared fixtures for bulkgen integration tests."""
+
+from __future__ import annotations
+
+from collections.abc import Callable
+from pathlib import Path
+
+import pytest
+import yaml
+
+from bulkgen.config import ProjectConfig, load_config
+
+WriteConfig = Callable[[dict[str, object]], ProjectConfig]
+
+
+@pytest.fixture
+def project_dir(tmp_path: Path) -> Path:
+    """A temporary directory acting as the project root."""
+    return tmp_path
+
+
+@pytest.fixture
+def write_config(project_dir: Path) -> WriteConfig:
+    """Write a bulkgen YAML config and return the loaded ProjectConfig.
+
+    Usage::
+
+        config = write_config({"targets": {"out.txt": {"prompt": "hello"}}})
+    """
+
+    def _write(raw: dict[str, object]) -> ProjectConfig:
+        config_path = project_dir / "project.bulkgen.yaml"
+        _ = config_path.write_text(yaml.dump(raw, default_flow_style=False))
+        return load_config(config_path)
+
+    return _write
+
+
+@pytest.fixture
+def simple_text_config(write_config: WriteConfig) -> ProjectConfig:
+    """A minimal config with one text target."""
+    return write_config({"targets": {"output.txt": {"prompt": "Generate something"}}})
+
+
+@pytest.fixture
+def multi_target_config(project_dir: Path, write_config: WriteConfig) -> ProjectConfig:
+    """Config with multiple targets forming a dependency chain.
+
+    input.txt (external file) -> summary.md -> final.txt
+    Also has an independent image target: hero.png
+    """
+    _ = (project_dir / "input.txt").write_text("Some input content")
+    return write_config(
+        {
+            "targets": {
+                "summary.md": {
+                    "prompt": "Summarize the input",
+                    "inputs": ["input.txt"],
+                },
+                "final.txt": {
+                    "prompt": "Finalize the summary",
+                    "inputs": ["summary.md"],
+                },
+                "hero.png": {
+                    "prompt": "A heroic landscape",
+                    "width": 1024,
+                    "height": 768,
+                },
+            }
+        }
+    )
+
+
+@pytest.fixture
+def prompt_file(project_dir: Path) -> Path:
+    """Create a prompt file on disk and return its path."""
+    p = project_dir / "my_prompt.txt"
+    _ = p.write_text("This prompt comes from a file")
+    return p