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-ag3nt/src/prompt.rs

@@ -318,7 +318,7 @@ shared closer
         let rendered = render(
             &PRODUCTION_TEMPLATE,
             Flavor::Manager,
-            "hm1nd",
+            "root",
             "she/her",
             None,
             None,
@@ -346,7 +346,7 @@ shared closer
         let manager = render(
             &PRODUCTION_TEMPLATE,
             Flavor::Manager,
-            "hm1nd",
+            "root",
             "she/her",
             None,
             None,
@@ -390,7 +390,7 @@ You are hyperhive agent `{label}` (qualified: `{qualified_label}`){hive_identity
         let rendered = render(
             IDENTITY_FIXTURE,
             Flavor::Manager,
-            "hm1nd",
+            "root",
             "she/her",
             None,
             Some("constellat1on"),