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/reminder_scheduler.rs

@@ -172,7 +172,7 @@ pub fn write_payload(agent: &str, host_path: &Path, message: &str) -> Result<(),
 /// under. Every agent sees its state at `/agents/<container>/state/`
 /// (see `lifecycle::set_nspawn_flags`). Auto-file paths use the same
 /// prefix so the round-trip is symmetric. The manager logical name
-/// maps to its container name (`hm1nd`) per `lifecycle::MANAGER_NAME`.
+/// maps to its container name (`root`) per `lifecycle::MANAGER_NAME`.
 #[must_use]
 pub fn container_state_prefix(agent: &str) -> String {
     if agent == hive_sh4re::MANAGER_AGENT {