chore: add project documentation framework

.project-docs/40-domain/business-rules.md

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+# Business Rules
+
+## Durable Rules
+
+- {business or product rule}
+
+## Open Questions
+
+- {rule that needs human confirmation}
+
+## Last Reviewed
+
+{YYYY-MM-DD}

.project-docs/40-domain/glossary.md

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+# Glossary
+
+| Term | Meaning | Notes |
+|---|---|---|