Summary

• add top-level non-sensitive blocker_summary to plan and audit JSON
• aggregate unpatchable text-object reasons, split kinds, split blocker reasons, and blocker fonts
• document the summary and mark M15 done in the roadmap

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

^{Need help on this PR? Tag @codesmith with what you need. Autofix is disabled.}