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

docs/getting-started/reinstall.md

@@ -142,9 +142,8 @@ sops updatekeys hosts/<hostname>/secrets.yaml
 Dann Konfiguration neu deployen:
 
 ```bash
-nixos-rebuild switch --flake .#<hostname> \
-  --target-host <user>@<IP> --use-remote-sudo \
-  --ssh-option="-p 2299"
+NIX_SSHOPTS="-p 2299" nixos-rebuild switch --flake .#<hostname> \
+  --target-host <user>@<IP> --use-remote-sudo
 ```
 
 ## Häufige Probleme