fix(hierarchy): include transfer snapshots in replay content comparison

Review round 1 blocker: sameEvent omitted transferFrom/transferTo, so a
retried transfer re-routed to a different destination would silently
replay instead of conflicting. Transfer source/destination are semantic
event content per §5.2. Adds a witness varying the transfer destination
on a duplicate idempotency key; also fixes a stale cross-reference in
the db witness header.

packages/db/src/hierarchy-audit.witness.test.ts

@@ -9,7 +9,7 @@
  * table — events survive the deletion of their target), the causation
  * self-FK, and the outbox's FK/uniqueness/status shape. The repository-level
  * half of §6.4 (same-transaction atomicity, rollback, replay) is witnessed in
- * apps/gateway/src/hierarchy/hierarchy-audit.witness.test.ts.
+ * apps/gateway/src/hierarchy/hierarchy-audit.integration.test.ts.
  *
  * Two legs run the same witness body:
  *  - PGlite (WASM Postgres): always runs.