chore: update Nix configurations for Nixcloud and common hosts

- Add Nixcloud host configurations including networking, hardware, and system settings
- Refactor existing configurations for clarity and organization
- Remove unused podman configuration from home-manager
- Update SSH agent settings and session variables in Nixbook host

hosts/common/users/nimbus/default.nix

@@ -0,0 +1,44 @@
+{ pkgs, config, ... }:
+let
+  ifTheyExist = groups: builtins.filter (group: builtins.hasAttr group config.users.groups) groups;
+in
+{
+  users.users.nimbus = {
+
+    isNormalUser = true;
+    initialPassword = "changeme";
+    extraGroups = [
+      "fuse"
+      "networkmanager"
+      "scard"
+      "wheel"
+    ]
+    ++ ifTheyExist [
+      "docker"
+      "git"
+      "i2c"
+      "kvm"
+      "libvirt"
+      "libvirtd"
+      "photos"
+      "scanner"
+      "video"
+      "wireshark"
+    ];
+    openssh.authorizedKeys.keyFiles = [
+      (builtins.fetchurl {
+        url = "https://meta.sr.ht/~sposito.keys";
+        name = "sposito-srht-keys";
+        sha256 = "1mf76x36kd1iaccy6l5f5xnbjqkm1fwf9giws9nb3bvgmj3c25wc";
+      })
+    ];
+
+    packages = with pkgs; [
+      git
+      podman
+      podman-compose
+      nginx
+    ];
+  };
+
+}