Merge feat/remote-builders into uconsole-cm5-incremental

Bidirectional remote building + rename uconsole-cm5 -> uConsole:
- Rename all uconsole-cm5 refs to uConsole (nixosSystem key, paths, module)
- Replace single-machine remote-builder module with multi-machine config
- Enable remote builder on lazyworkhorse -> uConsole (aarch64)
- Enable remote builder on uConsole -> lazyworkhorse (x86_64)
- Add builder system user + SSH key via agenix-rekey (secrets/builder_key.age)
- Add builder_key + gortium_password age secrets to all hosts
- Fix pre-existing bugs: missing modules in lazyworkhorse/cyt-pi,
  SSH config structure (hostKeys outside settings), cyt-pi inline user
- Remove obsolete openclaw-node service + module + age secrets

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" "usb_storage" "sdhci_pci" "nvme" ];
+  boot.initrd.kernelModules = [ ];
+  boot.extraModulePackages = [ ];
+
+  # SD card partitions (nixos-uconsole layout)
+  fileSystems."/" = {
+    device = "/dev/disk/by-label/NIXOS_SD";
+    fsType = "ext4";
+    options = [ "noatime" ];
+  };
+
+  fileSystems."/boot/firmware" = {
+    device = "/dev/disk/by-label/FIRMWARE";
+    fsType = "vfat";
+    options = [ "fmask=0022" "dmask=0022" ];
+  };
+
+  swapDevices = [ ];
+
+  nixpkgs.hostPlatform = lib.mkDefault "aarch64-linux";
+  hardware.enableRedistributableFirmware = true;
+  powerManagement.cpuFreqGovernor = lib.mkDefault "ondemand";
+}