feat(hosts): make config multi-host and add vps host

Parametrize networking, users, and containers modules under
myNetworking/myUsers/myContainers so both hosts share the same logic
instead of duplicating it, and split desktop/server module imports
into modules/profiles/. Adds hosts/vps (not installed yet, hardware
config and bootloader device are placeholders) to run Traefik,
Headscale, Headplane, and Gitea via a combined Docker Compose stack.

Wires up agenix for secrets and migrates miku-homelab's WireGuard
private key off a plain filesystem path into an encrypted
secrets/miku-homelab-wg.age. The vps side of that tunnel still needs
its own key generated and encrypted after install.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

modules/profiles/desktop.nix

@@ -0,0 +1,12 @@
+{
+  imports = [
+    ../desktop/firefox.nix
+    ../desktop/plasma.nix
+    ../system/gaming.nix
+    ../system/audio.nix
+    ../system/graphics.nix
+    ../system/fonts.nix
+    ../security/secureboot.nix
+    ../services/flatpak.nix
+  ];
+}