refactor: Move network configurations to machine directories

- Move network-congenital-optimist.nix to machines/congenital-optimist/
- Move network-sleeper-service.nix to machines/sleeper-service/
- Update import paths in machine configurations
- Clean up modules/network/common.nix to remove SSH duplication
- Consolidate SSH configuration in modules/security/ssh-keys.nix
- Remove machine-specific networking from shared common module

This improves dependency tracking by co-locating machine-specific
network configurations with their respective machines.

machines/congenital-optimist/configuration.nix

@@ -7,7 +7,7 @@
 }: {
   imports = [
     ./hardware-configuration.nix
-    ../../modules/network/network-congenital-optimist.nix
+    ./network-congenital-optimist.nix
     
     # Security modules
     ../../modules/security/ssh-keys.nix

machines/congenital-optimist/network-congenital-optimist.nix

@@ -0,0 +1,21 @@
+# Networking Configuration - congenital-optimist
+# AMD Threadripper workstation network setup
+{ config, pkgs, ... }:
+
+{
+  imports = [
+    ../../modules/network/common.nix
+  ];
+
+  # Machine-specific network configuration
+  networking = {
+    hostName = "congenital-optimist";
+    hostId = "8425e349";
+    networkmanager.enable = true;
+    
+    # Additional firewall ports for workstation services
+    firewall.allowedTCPPorts = [ 
+    ];
+  };
+
+}