DOC: Adopt from dandi-cli - rudimentary CLAUDE.md and pytest_plugin.py (summary of depends, ai_generated marker, better diff for DandiBaseModel)

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Repo Overview
+- `dandischema` is a pure-Python library defining the DANDI metadata schemata (no CLI).
+- Source lives under `dandischema/`, tests under `dandischema/tests/`.
+- Helper scripts (schema publishing, license fetching, etc.) live under `tools/`.
+- `pyproject.toml` is the single source of truth for dependencies and tool config; `tox.ini` orchestrates testing/linting; `.pre-commit-config.yaml` runs auto-formatters.
+
+## Build/Test Commands
+- Run full test suite: `tox -e py3` (or `tox -e py` to use the active interpreter).
+- Run a single test: `tox -e py3 -- dandischema/tests/test_models.py::test_function -v`.
+- Inside an active venv (`uv venv` / `source .venv/bin/activate`): `python -m pytest dandischema`.
+- Lint: `tox -e lint` (runs `codespell` + `flake8` over `dandischema/`).
+- Type checking: `tox -e typing` (runs `mypy dandischema`).
+- Lint + types together: `tox -e lint,typing`.
+- Set `DANDI_TESTS_NONETWORK=1` to make tests refuse outbound HTTP (the `disable_http` autouse fixture in `dandischema/tests/conftest.py` points proxies at a dead address).
+- DataCite-dependent tests require `DATACITE_DEV_LOGIN` / `DATACITE_DEV_PASSWORD`; set `NO_ET=1` to disable etelemetry. Both are passed through by tox.
+- There is no `docker-compose` in this repo and no `hatch run test:run` env — don't suggest those (the dandi-cli pattern doesn't apply here).
+
+## Pre-commit
+- Install hooks if missing (no `.git/hooks/pre-commit` present): `pre-commit install`.
+- Hooks run: trailing-whitespace, end-of-file-fixer, check-yaml, check-added-large-files, black, isort, codespell, flake8.
+- If a commit fails because hooks auto-fixed files, just re-run `git commit` — the second attempt usually succeeds. Investigate further only if it fails twice.
+
+## Test Markers
+- Mark AI-generated tests with `@pytest.mark.ai_generated`.
+- This project does **not** have a `pytest_plugin.py`. If a new marker is introduced, register it under a `[pytest]`/`markers =` block in `tox.ini` (or via `pytest.ini`/`conftest.py`) — otherwise `filterwarnings = error` (set in `tox.ini`) will turn the unregistered-marker warning into a failure.
+
+## Code Style
+- Black-formatted, line length 100 (see `.flake8: max-line-length = 100`; flake8 ignores `E203,W503`).
+- isort with `profile = "black"`, `force_sort_within_sections = true`, `reverse_relative = true`, `known_first_party = ["dandischema"]`.
+- Type annotations required for all new code — `mypy` runs in strict-ish mode (`allow_untyped_defs = false`, `warn_return_any`, `warn_unreachable`, `pydantic.mypy` plugin enabled). Models use Pydantic v2 (`pydantic[email]~=2.4`).
+- Class names: CamelCase; functions/variables: snake_case.
+- Exception names end with `Error` (see `dandischema/exceptions.py`).
+- Docstrings in NumPy style for public APIs; keep them in sync with signature changes.
+- Prefer specific exceptions over generic ones.
+- Imports organized stdlib / third-party / local, alphabetical within groups (isort handles ordering).
+- All imports at module top — no function-local imports (per global rule), unless guarding an optional dep with `try/except ImportError`.
+
+## Schema / Data Files
+- `dandischema/*.yaml` (e.g. `standards.yaml`, `model_standards.yaml`, `personinfo.yaml`) are tracked schema/data inputs — don't reformat or rename casually; downstream consumers and `tools/pubschemata.py` rely on them.
+- `dandischema/_version.py` is generated by `versioningit` (see `[tool.versioningit.write]`); don't edit by hand.