feat(nixos): consolidate hosts into a shared flake

Manage T450s, X1EG2 and Framework 13 from pinned NixOS inputs while retaining
machine-specific storage and hardware configuration.

Changes:

Shared Configuration:
- Extract common, KDE, desktop, development and Steam modules
- Share Emacs, VS Code, htop, DevOps tools and Docker across hosts
- Remove obsolete apps and global project language runtimes

Framework:
- Import the 11th-generation Intel hardware profile
- Enable Steam and ZFS with tookland/home mounted at /home
- Document manual ext4 root and ZFS installation steps
- Require installer-generated hardware configuration before installation

Validation:
- Evaluate both ThinkPads and Framework with test hardware
- Check Nix syntax, formatting and whitespace

hosts/x1eg2/hardware-configuration.nix

@@ -0,0 +1,46 @@
+# Do not modify this file!  It was generated by ‘nixos-generate-config’
+# and may be overwritten by future invocations.  Please make changes
+# to /etc/nixos/configuration.nix instead.
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  imports =
+    [ (modulesPath + "/installer/scan/not-detected.nix")
+    ];
+
+  boot.initrd.availableKernelModules = [ "xhci_pci" "nvme" "usb_storage" "sd_mod" "sdhci_pci" "battery" ];
+  boot.initrd.kernelModules = [ ];
+  boot.kernelModules = [ "kvm-intel" ];
+  boot.extraModulePackages = [ ];
+
+  fileSystems."/" =
+    { device = "rpool/root";
+      fsType = "zfs";
+    };
+
+  fileSystems."/home" =
+    { device = "rpool/home";
+      fsType = "zfs";
+    };
+
+  fileSystems."/boot" =
+    { device = "/dev/disk/by-uuid/BF51-953A";
+      fsType = "vfat";
+    };
+
+  swapDevices =
+    [ { device = "/dev/disk/by-uuid/a468fc29-ad58-474b-ac91-abc40d3567b3"; }
+    ];
+
+  # Enables DHCP on each ethernet and wireless interface. In case of scripted networking
+  # (the default) this is the recommended approach. When using systemd-networkd it's
+  # still possible to use this option, but it's recommended to use it in conjunction
+  # with explicit per-interface declarations with `networking.interfaces.<interface>.useDHCP`.
+  networking.useDHCP = lib.mkDefault true;
+  # networking.interfaces.enp0s31f6.useDHCP = lib.mkDefault true;
+  # networking.interfaces.wlp82s0.useDHCP = lib.mkDefault true;
+  networking.hostId = "7330cb06";
+
+  nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
+  hardware.cpu.intel.updateMicrocode = lib.mkDefault config.hardware.enableRedistributableFirmware;
+}