programs.git.enable + harness PATH tracks systemPackages

- harness-base.nix: switch to programs.git for declarative gitconfig.
- agent + manager service path = /run/current-system/sw → agents pick up
  new packages from their own agent.nix without harness edits.
- generated applied/<name>/flake.nix overrides programs.git.config.user
  (no more raw etc.gitconfig collision).

nix/templates/manager.nix

@@ -15,10 +15,11 @@
       HIVE_LABEL = "hm1nd";
       SHELL = "${pkgs.bashInteractive}/bin/bash";
     };
-    path = [
-      pkgs.claude-code
-      pkgs.bashInteractive
-    ];
+    # See note in agent-base.nix — `/run/current-system/sw` makes the
+    # harness service PATH track `environment.systemPackages` so anything
+    # an agent adds to its own `agent.nix` is visible without editing the
+    # service definition.
+    path = [ "/run/current-system/sw" ];
     serviceConfig = {
       ExecStart = "${pkgs.hyperhive}/bin/hive-m1nd serve";
       Restart = "on-failure";