fix: desktop-only safety fixes (nix-bitcoin compat, mkForce, conditional caddy)

1. Add nix-bitcoin.generateSecrets = lib.mkDefault true global compat
   default in role-logic.nix so Desktop Only systems can evaluate while
   nix-bitcoin is still globally imported by the flake.

2. Harden Desktop Only role: change all server/node service and feature
   disables from lib.mkDefault false to lib.mkForce false so they cannot
   be overridden by custom.nix or option defaults.
   - sovran_systemsOS.services: synapse, bitcoin, vaultwarden, wordpress, nextcloud
   - sovran_systemsOS.features: haven, mempool, element-calling, bitcoin-core
   - sovran_systemsOS.web.btcpayserver

3. Make Caddy conditional in caddy.nix:
   enable = needsHttpsPorts || extraVhosts != ""
   so Caddy does not run on Desktop Only installs with no web services.

modules/core/caddy.nix

@@ -16,7 +16,10 @@ let
 in
 {
   services.caddy = {
-    enable = true;
+    # Only enable Caddy when at least one domain-based service needs it or
+    # the operator has defined custom vhosts.  This prevents Caddy from
+    # running on Desktop Only installs that have no web services configured.
+    enable = needsHttpsPorts || extraVhosts != "";
     user = "caddy";
     group = "root";
   };

modules/core/role-logic.nix

@@ -3,6 +3,13 @@
 {
   config = lib.mkMerge [
 
+    # nix-bitcoin is globally imported by the flake (nixosModules.Sovran_SystemsOS).
+    # This default satisfies nix-bitcoin's generateSecrets assertion so that Desktop
+    # Only systems can evaluate without enabling any Bitcoin services.
+    {
+      nix-bitcoin.generateSecrets = lib.mkDefault true;
+    }
+
     # ── Server+Desktop Role (default) ─────────────────────────
     (lib.mkIf config.sovran_systemsOS.roles.server_plus_desktop {
       sovran_systemsOS.web.btcpayserver = lib.mkDefault true;
@@ -12,15 +19,24 @@
     (lib.mkIf config.sovran_systemsOS.roles.desktop {
       services.desktopManager.gnome.enable = true;
 
+      # Force all server/node services and features off so they cannot be
+      # accidentally enabled via custom.nix or option defaults on Desktop Only.
       sovran_systemsOS.services = {
-        synapse = lib.mkDefault false;
+        synapse = lib.mkForce false;
-        bitcoin = lib.mkDefault false;
+        bitcoin = lib.mkForce false;
-        vaultwarden = lib.mkDefault false;
+        vaultwarden = lib.mkForce false;
-        wordpress = lib.mkDefault false;
+        wordpress = lib.mkForce false;
-        nextcloud = lib.mkDefault false;
+        nextcloud = lib.mkForce false;
       };
 
-      sovran_systemsOS.web.btcpayserver = lib.mkDefault false;
+      sovran_systemsOS.features = {
+        haven = lib.mkForce false;
+        mempool = lib.mkForce false;
+        element-calling = lib.mkForce false;
+        bitcoin-core = lib.mkForce false;
+      };
+
+      sovran_systemsOS.web.btcpayserver = lib.mkForce false;
     })
 
     # ── Bitcoin Node Only Role ────────────────────────────────