docs: restore drill passed — S3 leg gate closed

18/18 instances replicated, restic seed complete and restore-tested
(tree identical to live; dump loads into a scratch MariaDB, 12/12
tables). Remaining ks2 gates are the nuc leg after FTTH.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ks4/restic-backup.md

@@ -283,8 +283,10 @@ deleted.
   nextcloud tree, churn-independent; restic: seed at 60–115 MiB/s,
   local-cache incrementals). Details in
   [plakar-s3-data.md](plakar-s3-data.md).
-- **Left to do**: restore test on the complete `restic-data`; re-enable
-  the interim ks2 push until FTTH; then the ks2 decommission gates
+- **Done 2026-08-28**: initial sync (1,114,212 files / 1.239 TiB in
+  4h10m, only 2.4 GiB added thanks to dedup + the seafile GC), restore
+  drill passed (§7), interim ks2 push re-enabled.
+- **Left**: the nuc leg after FTTH, then the ks2 decommission
   ([../ks2/plan.md](../ks2/plan.md)). The instance leg (§6) is
   shelved, not pending.
 - **Old tool**: see the legacy note above; the `integration-incus`