chore: add project documentation framework

.project-docs/10-decisions/decision-index.md

@@ -0,0 +1,22 @@
+# Decision Index
+
+## Active Decisions
+
+| ID | Decision | Status | Date | Applies To | Detail |
+|---|---|---|---|---|---|
+
+## Superseded Decisions
+
+| ID | Decision | Superseded By | Date |
+|---|---|---|---|
+
+## Decision Criteria
+
+Create or update an ADR when a choice affects:
+
+- project positioning
+- architecture boundaries
+- public behavior
+- data model
+- long-term maintenance
+- user-facing workflow