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.

hive-c0re/src/agent_config/topology.rs

@@ -192,7 +192,10 @@ mod tests {
 
     #[test]
     fn all_agents_in_returns_every_name_sorted() {
-        assert_eq!(all_agents_in(&roster_three()), vec!["alice", "bob", "carol"]);
+        assert_eq!(
+            all_agents_in(&roster_three()),
+            vec!["alice", "bob", "carol"]
+        );
     }
 
     #[test]