Fix btcpayserver.nix to use pkgs.stable overlay

Replace all pkgs-stable references with pkgs.stable (from overlay-stable in flake.nix):
- Remove pkgs-stable from function arguments
- Use pkgs.stable.nbxplorer (2.6.10 from nixos-26.05)
- Use pkgs.stable.btcpayserver (2.4.2 from nixos-26.05)

flake.nix

@@ -1,32 +1,68 @@
 {
-  description = "Sovran Systems OS - A secure, self-hosted server OS";
+	description = "The Ultimate Sovran_SystemsOS Configuration from Sovran Systems";
 
 	inputs = {
 		nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
-    nixpkgs-stable.url = "github:nixos/nixpkgs/nixos-26.05";
 		nixvim.url = "github:nix-community/nixvim";
 		btc-clients.url = "github:emmanuelrosa/btc-clients-nix";
+		nixpkgs-stable.url = "github:nixos/nixpkgs/nixos-26.05";
 	};
 
-  outputs = { self, nixpkgs, nixpkgs-stable, nixvim, btc-clients }:
+	outputs = { self, nixpkgs, nixvim, btc-clients, nixpkgs-stable, ... }:
+
 	let
-      system = "x86_64-linux";
-      pkgs = nixpkgs.legacyPackages.${system};
-      pkgs-stable = import nixpkgs-stable {
-        inherit system;
+		overlay-stable = final: prev: {
+			stable = import nixpkgs-stable {
+				system = prev.stdenv.hostPlatform.system;
 				config.allowUnfree = true;
 			};
+		};
 	in
 	{
 		nixosConfigurations.nixos = nixpkgs.lib.nixosSystem {
-        inherit system;
-        specialArgs = { inherit pkgs-stable; };
 			modules = [
-          ./configuration.nix
-          ./modules
-          btc-clients.nixosModules.bitcoin
+				{ nixpkgs.hostPlatform = "x86_64-linux"; nixpkgs.overlays = [ overlay-stable ]; }
+				self.nixosModules.Sovran_SystemsOS
+				./hardware-configuration.nix
+				./role-state.nix
+				./custom.nix
+			];
+		};
+
+		nixosConfigurations.sovran_systemsos-iso = nixpkgs.lib.nixosSystem {
+			modules = [
+				{ nixpkgs.hostPlatform = "x86_64-linux"; nixpkgs.overlays = [ overlay-stable ]; }
+				./iso/common.nix
+				./modules/bitcoin
 				nixvim.nixosModules.nixvim
 			];
 		};
+
+		nixosModules.Sovran_SystemsOS = { pkgs, lib, config, ... }: {
+			imports = [
+				({ config, pkgs, ... }: {
+					nixpkgs.overlays = [ overlay-stable ];
+				})
+				./configuration.nix
+				./modules/bitcoin
+				nixvim.nixosModules.nixvim
+			];
+			config = {
+				environment.systemPackages = with pkgs; [
+					btc-clients.packages.${pkgs.system}.bisq
+					btc-clients.packages.${pkgs.system}.bisq2
+					btc-clients.packages.${pkgs.system}.sparrow
+				];
+			};
+		};
+
+		nixosTests.nwc-wallets-port-collision =
+			import ./nix/tests/nwc-wallets-port-collision.nix {
+				inherit nixpkgs;
+				system = "x86_64-linux";
+			};
+
+		checks.x86_64-linux.nwc-wallets-port-collision =
+			self.nixosTests.nwc-wallets-port-collision;
 	};
 }

modules/bitcoin/btcpayserver.nix

@@ -1,4 +1,4 @@
-{ config, lib, pkgs, pkgs-stable, ... }:
+{ config, lib, pkgs, ... }:
 
 with lib;
 let
@@ -26,8 +26,8 @@ let
       };
       package = mkOption {
         type = types.package;
-        default = pkgs-stable.nbxplorer;
-        defaultText = "pkgs-stable.nbxplorer";
+        default = pkgs.stable.nbxplorer;
+        defaultText = "pkgs.stable.nbxplorer";
         description = "The package providing nbxplorer binaries.";
       };
       dataDir = mkOption {
@@ -47,7 +47,7 @@ let
       # be nix-bitcoin <=0.0.91)
       addNetworkSymlink = mkOption {
         readOnly = true;
-        default = pkgs-stable.nbxplorer != cfg.nbxplorer.package;
+        default = pkgs.stable.nbxplorer != cfg.nbxplorer.package;
         description = ''
           Whether to add a compatibility symlink (like `${cfg.nbxplorer.dataDir}/Main`)
           to the dataDir.
@@ -83,8 +83,8 @@ let
       };
       package = mkOption {
         type = types.package;
-        default = pkgs-stable.btcpayserver;
-        defaultText = "pkgs-stable.btcpayserver";
+        default = pkgs.stable.btcpayserver;
+        defaultText = "pkgs.stable.btcpayserver";
         description = "The package providing BTCPay Server binaries.";
       };
       address = mkOption {