Prepare v0.1.6 release

[ecochran76]

Summary

• bump package and CLI versions to 0.1.6
• finalize changelog notes for the M14 length-position coverage release

Validation

• python3 -m py_compile pdf_glyph_replace.py pdf_fixture.py pdf_inventory.py pdf_dogfood.py pdf_dogfood_summary.py pdf_mutation/*.py
• python3 -m unittest discover -s tests -v
• release-venv install, console --version checks, wheel build
• release checklist public length-changing smoke with qpdf --check, pdftotext, bbox alignment assertions, and checked_edge/checked_delta verification

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