rename(#162): scrub remaining hm1nd references from comments and MCP instructions

All functional renames (MANAGER_NAME, MANAGER_AGENT → "root") were done in
earlier commits. This cleans up the stale `hm1nd` strings that remained in
doc comments, test fixture labels, and the manager MCP server instructions
(which told the manager its config lived at /agents/hm1nd/config/agent.nix).

hive-c0re/src/agent_ports.rs

@@ -84,7 +84,7 @@ mod tests {
     #[test]
     fn build_map_filters_manager() {
         // Use MANAGER_NAME in the input so the assert below actually
-        // exercises the filter path — a literal `"hm1nd"` would pass
+        // exercises the filter path — a literal `"root"` would pass
         // trivially if the constant ever changed and the filter
         // silently became a no-op.
         let names: Vec<String> = ["iris", MANAGER_NAME, "argus"]