feat(home-manager): add core+extras profile and wire it into vps

Introduce myHomeProfile.extraPrograms (mirrors myPackages.extra) so each
host's NixOS config declares which extra Home Manager modules it needs
on top of a shared core (fish, starship, btop, git). miku-homelab's
former home.nix becomes its extras list; vps gets home-manager for the
first time using core alone.

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

modules/system/home-profile.nix

@@ -0,0 +1,8 @@
+{ lib, ... }:
+{
+  options.myHomeProfile.extraPrograms = lib.mkOption {
+    type = lib.types.listOf lib.types.path;
+    default = [ ];
+    description = "Extra Home Manager modules to import for this user, on top of the core profile.";
+  };
+}