content: tree-CRDT orphan reparenting (no content loss on concurrent delete-section) + 4 tests (742/742)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/content/scoreboard.json

@@ -34,7 +34,7 @@
     "store": {"pass": 29, "fail": 0},
     "snapshot": {"pass": 20, "fail": 0},
     "crdt": {"pass": 34, "fail": 0},
-    "crdt-tree": {"pass": 17, "fail": 0},
+    "crdt-tree": {"pass": 21, "fail": 0},
     "crdt-blocks": {"pass": 7, "fail": 0},
     "crdt-store": {"pass": 14, "fail": 0},
     "sync": {"pass": 14, "fail": 0},
@@ -42,7 +42,7 @@
     "md-doc": {"pass": 12, "fail": 0},
     "fed": {"pass": 20, "fail": 0}
   },
-  "total_pass": 738,
+  "total_pass": 742,
   "total_fail": 0,
-  "total": 738
+  "total": 742
 }