feat: add uConsole CM5 host configuration

- Add nixos-uconsole and nixos-hardware inputs for CM5/RPi5 support
- Create hosts/uconsole/configuration.nix with HAM radio, SDR, and security tools
- Create hosts/uconsole/hardware-configuration.nix for CM5 hardware
- Register uConsole in flake.nix nixosConfigurations
- Add uconsole host key placeholder to lib/keys.nix

hosts/uconsole/hardware-configuration.nix

@@ -0,0 +1,30 @@
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  imports =
+    [ (modulesPath + "/installer/scan/not-detected.nix")
+    ];
+
+  boot.initrd.availableKernelModules = [ "xhci_pci" "usbhid" "sdhci_pci" ];
+  boot.initrd.kernelModules = [ ];
+  boot.kernelModules = [ ];
+  boot.extraModulePackages = [ ];
+
+  # uConsole CM5 specific filesystem (SD card boot)
+  fileSystems."/" =
+    { device = "/dev/disk/by-label/NIXOS_SD";
+      fsType = "ext4";
+      options = [ "noatime" ];
+    };
+
+  fileSystems."/boot" =
+    { device = "/dev/disk/by-label/FIRMWARE";
+      fsType = "vfat";
+    };
+
+  swapDevices = [ ];
+
+  # uConsole CM5 is ARM64
+  nixpkgs.hostPlatform = lib.mkDefault "aarch64-linux";
+  hardware.enableRedistributableFirmware = true;
+}