Retire dotfiles-rebuild, switch to dm-pull-deploy push timer

- Drop modules/dotfiles-rebuild.nix and its imports in clan.nix;
  sunken-ship + phantom-ship no longer ship the legacy 15-min
  rebuild-from-git timer.
- Add dm-pull-deploy-push systemd timer on sunken-ship: every 15min
  runs dm-send-deploy to announce origin/main rev via data-mesher
  gossip (sunken is the dm-pull-deploy push node).
- Fix mulbo-pull service path: add openssh so 'git fetch' over an
  SSH remote stops failing with 'cannot run ssh'.
- vps-relay authorized_keys: rename Mac key comment to mac-admin,
  add sunken-ship's actual ed25519 key for ZT mesh debugging.
- home.nix: add cinny-desktop (Matrix client).
- neovim: enable cursorline.

flake-modules/clan.nix

@@ -125,7 +125,6 @@ in {
         }
         clanHostsModule
         ../nixos/hosts/sunken-ship.nix
-        config.flake.nixosModules.dotfiles-rebuild
         config.flake.nixosModules.server-debug-tools
         config.flake.nixosModules.monitoring-node-exporter
         config.flake.nixosModules.monitoring-prometheus-server
@@ -169,7 +168,6 @@ in {
         inputs.nix-openclaw.nixosModules.openclaw-gateway
         inputs.catppuccin.nixosModules.catppuccin
         ../nixos/hosts/phantom-ship.nix
-        config.flake.nixosModules.dotfiles-rebuild
         config.flake.nixosModules.server-debug-tools
         config.flake.nixosModules.monitoring-node-exporter
         inputs.home-manager.nixosModules.home-manager

flake-modules/nixos-modules.nix

@@ -1,9 +1,8 @@
 # Expose reusable NixOS modules via `flake.nixosModules`.
 #
 # Consume from a host's flake-module via:
-#   modules = [ config.flake.nixosModules.dotfiles-rebuild ];
+#   modules = [ config.flake.nixosModules.server-debug-tools ];
 { ... }: {
-  flake.nixosModules.dotfiles-rebuild = ../modules/dotfiles-rebuild.nix;
   flake.nixosModules.server-debug-tools = ../modules/server-debug-tools.nix;
   flake.nixosModules.monitoring-node-exporter = ../modules/monitoring-node-exporter.nix;
   flake.nixosModules.monitoring-prometheus-server = ../modules/monitoring-prometheus-server.nix;