add deploy/create/install apps, fix templates and docs

- Add apps: create (scaffold host from template), deploy (multi-host
  deployment with -n filter), install (NixOS installation from live ISO)
- Register all apps in flake.nix (create, deploy, install, rebuild)
- Add deploy.json config (cryodev-main, SSH port 2299)
- Fix generic-server template: was using Pi hardware/boot config,
  now correct x86_64 with systemd-boot, UEFI, ROOT/BOOT/SWAP labels
- Fix template networking.nix: use HOSTNAME placeholder instead of
  hardcoded cryodev-pi (both templates)
- Fix headplane upstream pnpm-deps hash mismatch via overlay
- Fix all docs: replace root@ with user@, --ssh-option with
  NIX_SSHOPTS, add deploy app references, update first-install guide
  to use create app and document service deactivation steps

templates/generic-server/boot.nix

@@ -1,8 +1,7 @@
 {
-  boot = {
-    loader = {
-      grub.enable = false;
-      generic-extlinux-compatible.enable = true;
-    };
+  boot.loader.systemd-boot = {
+    enable = true;
+    configurationLimit = 10;
   };
+  boot.loader.efi.canTouchEfiVariables = true;
 }