Refactor DMS configuration and introduce home-manager integration

- Simplified `default.nix` by removing legacy home-manager settings and delegating them to a new `_private/hm.nix` module for better organization.
- Added a new script `dms-restart-once.sh` to handle service restarts and cache management for DMS plugins.
- Updated the DMS configuration to streamline the integration of third-party plugins and improve overall modularity.

flake.nix

@@ -207,7 +207,7 @@
       lib = inputs.nixpkgs.lib;
       # import-tree default: only .nix, skip paths with /_/ (see
       # https://import-tree.oeiuwq.com/guides/filtering/ ). filterNot composes AND with that.
-      # Skip /package/, /packages/, and dms/home-manager/ (callPackage + DMS HM colocation).
+      # Skip /package/ and /packages/ (callPackage colocation).
       # Avoid a global "/home-manager/" filter — it would drop modules/ssh/home-manager/.
       modulesTree =
         lib.pipe inputs.import-tree [
@@ -217,7 +217,6 @@
               p:
               lib.hasInfix "/package/" p
               || lib.hasInfix "/packages/" p
-              || lib.hasInfix "dms/home-manager/" p
             ))
           (it: it ./modules)
         ];