chore: add project documentation framework

.project-docs/90-maintenance/stale-items.md

@@ -0,0 +1,16 @@
+# Stale Items
+
+This is the integrated registry of stale or conflicting canonical memory. Update it only in Integration Gate.
+
+## Possibly Stale Or Conflicting
+
+| Date | Document | Issue | Source Task | Needed Confirmation |
+|---|---|---|---|---|
+
+## Missing Context
+
+- {missing information that affects future planning}
+
+## Feature Task Routing
+
+A feature task records new uncertainty in its own task record. When a separate conflict record is needed, write `90-maintenance/conflicts/{task_id}__<slug>.md`; do not append concurrent feature work here.