docs: spec system overhaul — frontmatter + lint + AGENTS.md + EARS infra #39

Job	Run time
Test (windows-latest / py3.12)	6m 39s
Build Linux abi3 wheel	3m 21s
Test (macos-latest / py3.12)	3m 32s
Test without extras (importorskip auto-skip)	3m 1s
Test slow (Linux / py3.12 — PDF)	3m 39s
Test (Linux / py3.11)	3m 58s
Test (Linux / py3.13)	3m 49s
Test (Linux / py3.12)	3m 53s
Test (Linux / py3.10)	4m 3s
All tests passed	4s
	35m 59s

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