docs: agent-hierarchy default-parent is root, not the manager

docs/agent-hierarchy.md

@@ -12,14 +12,18 @@ Topology lives in the hive-c0re-owned **meta repo**, alongside
 
 ```json
 {
-  "manager": null,
-  "alice":   "manager",
-  "bob":     "alice"
+  "ruth":  null,
+  "alice": null,
+  "bob":   "alice"
 }
 ```
 
-`null` = root-level agent. Today only the manager qualifies by default.
-Other agents land under `"manager"` on first sync. Re-parenting is
+`null` = root-level agent. New agents **default to root** (`null` parent) —
+there is no structural manager that everything hangs under. Hierarchy is
+built explicitly: an agent that requests a sub-agent gets a
+requester-as-parent edge written at its `init_config` approval (so `bob`
+above was spawned by `alice`), and the operator can reparent any agent. The
+bootstrap container (`ruth`) is just another root. Re-parenting is
 operator-driven:
 
 - CLI: `hive-c0re set-parent <child> --parent <new>` (or `--root` to