add CLAUDE.md with development instructions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: fedorov

CLAUDE.md

@@ -0,0 +1,50 @@
+# CLAUDE.md
+
+## Project
+
+pydcmqi — Python API wrapper for dcmqi (DICOM quantitative imaging) CLI tools.
+
+## Development
+
+- Python 3.10+
+- Uses `hatchling` + `hatch-vcs` for build/versioning
+- Install for development: `.venv/bin/pip install -e ".[test]"`
+- Pre-commit hooks configured (ruff, mypy, prettier, codespell, etc.)
+
+## Before committing
+
+Always run pre-commit hooks before committing:
+
+```bash
+.venv/bin/pre-commit run --all-files
+```
+
+Fix any failures before creating the commit. Do not skip hooks with `--no-verify`.
+
+## Testing
+
+```bash
+.venv/bin/pytest tests/
+```
+
+Integration tests (TestSegimageRead, TestSegimageWrite) require network access to download DICOM data from IDC.
+
+## Linting
+
+```bash
+.venv/bin/pre-commit run --all-files   # all hooks including mypy
+.venv/bin/ruff check src/ tests/       # ruff only
+.venv/bin/mypy src/ tests/             # mypy only
+```
+
+## Project structure
+
+```
+src/pydcmqi/
+├── __init__.py      # Public API exports
+├── types.py         # TypedDicts, Literal types
+├── exceptions.py    # DcmqiError
+├── triplet.py       # Triplet class (DICOM code triplet)
+├── segment.py       # SegmentData, Segment
+├── segimage.py      # SegImageData, SegImageFiles, SegImage (orchestrator)
+```