## Summary

Closes #897.

- Replace the 14 `dev_requirements/*.in/*.txt` files with PEP 735
`[dependency-groups]` in `pyproject.toml` (tests, coverage, type_check,
linting, formatting, packaging, json_schemas, docs, plus a `dev`
meta-group).
- Switch tox to `tox-uv`: `[testenv:*]` now use `dependency_groups = …`
instead of `deps = -r dev_requirements/…`. Editable install declared
once at `[testenv]` level via `package = editable`.
- Update CI: every `pip install tox` → `pip install tox tox-uv`. The two
workflow steps that bypassed tox (`python-publish.yml` and
`python-publish-scheduled.yml`) now use `pip install uv` + `uv pip
install --system --group …`.
- Drop the `/dev_requirements/` dependabot pip entry — the root entry
covers PEP 735 groups too.
- Lock pinned versions in `uv.lock` (133 packages, generated against the
new groups).
- README + `docs/contributing_guide.rst`: new "Entwicklungs-Setup"
section pointing at uv + tox-uv (replaces the stale link to
`python_template_repository`).

## Test plan

- [x] `tox -e tests` — 121 passed locally with `tox-uv`, editable bo4e
built via hatchling.
- [ ] `tox -e linting`
- [ ] `tox -e type_check`
- [ ] `tox -e coverage`
- [ ] `tox -e docs`
- [ ] CI: all matrix workflows green
- [ ] Dependabot picks up the runtime + PEP 735 groups from the root
entry on next run

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

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Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>