docs: retire the agent hierarchy from every page that described it

The topology doc keeps its filename and its second half (manager
special-casing, harness unit shape) — both are cross-referenced from
other pages and neither is about the parent field. Its first half is
rewritten: what topology.json is now, and a table of what the removal
took with it, so a reader who finds `<parent>` or `set-parent` in an old
issue thread learns it went away rather than moved.

The dashboard's tree-rendering section is marked dormant rather than
deleted: the walk is still in swarm.js and retiring it is the frontend
owner's call.

docs/turn-loop/mcp.md

@@ -29,15 +29,13 @@ are opt-in via the P3RM1SS10NS tab.
 `recv(max?)`, `ack_until(up_to)`.
 
 - `send` — message a peer (logical name) or the operator
-  (`to: "operator"`). Use `to: "<parent>"` to address the topology
-  parent without hardcoding the label; the broker resolves the
-  sentinel at delivery time. Optional `in_reply_to: i64` links the
+  (`to: "operator"`). Optional `in_reply_to: i64` links the
   message to a prior id for thread rendering. Per-agent
   `services.hyperhive.agent.allowedRecipients` (default: empty = unrestricted) limits
   which names `send` accepts — useful for sandboxing: set
-  `[ "operator" ]` to restrict a sub-agent to operator messages only
-  (the topology parent is always reachable regardless of this list —
-  that carve-out is structural, keyed on parent relationship, not name).
+  `[ "operator" ]` to restrict a sub-agent to operator messages only.
+  The operator stays reachable regardless of this list, so an agent can
+  always report a block.
 - `recv` — drain inbox. Always an immediate peek, never blocks. `max`
   (default 1, cap 5) drains up to N rows. `recv` prefixes each returned row
   with `[msg #<id>]` (broker row id; note the highest id seen, then pass