Add CAS-safe task transitions and opt-in quality modules (#5)

Adds ABA-safe status transitions, zero-DDL opt-in quality modules, packaging coverage, and removes the internal tray receipt from the public tree.

Author: RMANOV

.gitignore

@@ -19,3 +19,8 @@ docs/press/
 # newly-created article not operator-reviewed (untrack from public repo)
 docs/articles/2026-05-09-convergent-evolution-vs-gbrain.md
 .claude/
+
+# Local product specifications and implementation concepts are private inputs.
+# Public branches contain code, tests, and separately approved marketing only.
+/.private-specs/
+/S2-READONLY-RECEIPT-2026-07-19.md