tests/frozen_clock.py fails without the [notebook] extra; checklist for the normalization pin move #262

This was found while reviewing morphobricks-normalization #88 (SWEEP-NM, merged as bbd9b6b).

1. Test hygiene. tests/frozen_clock.py _import_package() imports every module of the package, including notebook_axes and notebook_style. Those raise ImportError when matplotlib or ipywidgets are absent. So without the [notebook] extra, three tests fail:

• tests/test_description_write.py::test_a_frozen_clock_moved_by_a_day_…
• the two P30 cases in tests/test_spec_derived_design.py

CI installs the extra, so CI is green, but a plain pip install -e '.[dev]' run fails. There is no date dependence: it was checked across six simulated dates and four time zones. Fix: skip the notebook modules in _import_package() when the extra is missing, or make the dev extra pull in the notebook extra.

2. Checklist for moving the normalization pin to the release that carries #88 (PlaneRecord.position_id required, NM-04):

1. Tests: pass position_id= wherever a PlaneRecord is built:
   • tests/test_intensity.py, tests/test_report.py, tests/test_unchecked_channels.py, tests/test_notebook_debt.py;
   • tests/test_schema_v2_equivalence.py::test_step_4_…;
   • tests/simulation.py.
2. run/steps.py:229-231: remove the dead fill-in replace(r, position_id=entries[rel].position_id). A table without IDs is now refused by the reader, and run/reuse.py:130 already turns that into a full rebuild.
3. tests/test_run.py::test_table_without_position_ids_is_filled_without_reading: rewrite as "refused and rebuilt".
4. run/rows.py:33: position: str | None becomes str.
5. README.md:180: add position_id= to the PlaneRecord(...) example.
6. Bump the pin in pyproject.toml from @v0.3.4 and note it in the CHANGELOG.

With normalization #88 installed, all 28 failures and errors in preprocessing's suite are cases of item 1 or item 3.