feat(auth): streamline SOPS authentication and network configuration

- Replace age-based key decryption with automatic SSH host key support
- Simplify SSH configuration with consolidated host entries and enhanced security settings
- Upgrade home-manager to himmelblau for Microsoft Entra ID authentication
- Remove legacy agenix inputs and consolidate secrets to essential services only
- Add Cisco Secure Client overlay for enterprise VPN capabilities
- Update secrets.yaml to minimal configuration with gitea/github/hetzner services
- Expand system packages with tun module for VPN connectivity
- Add work directory setup for user development environment

hosts/default.nix

@@ -24,7 +24,9 @@
     "${mod}/services/gnome-services.nix"
     "${mod}/core/limine.nix"
     "${home}"
+    "${self}/work"
     inputs.sops-nix.nixosModules.sops
+    inputs.himmelblau.nixosModules.himmelblau
   ];
 in {
   flake.nixosConfigurations = {