refactor(flake): add user registry and multi-user host support

Separate user identity (data) from the reusable modules, and let a host
declare any number of users instead of exactly one.

- users/registry.nix: per-user identity (name, email, groups, authorized
  and signing keys) as the single source of identity; no user data is
  hardcoded in the modules.
- mkHost takes a `users` set keyed by username; per-user identity is
  injected into each home config via the `identity` module arg
  (extraSpecialArgs is per-host, so it cannot carry per-user data).
- modules/users.nix builds accounts from the registry; modules/ssh.nix no
  longer defines authorized keys (the registry owns them); home/git.nix
  and home/desktop.nix read `identity`; users/emmathorpe/work.nix drops
  its now-redundant git identity override.
- Restructure the tree: users/, home/, modules/, hosts/, lib/ replace the
  former lyrathorpe/ and system/ layout.
- Add standalone homeConfigurations (the portable subset: shell, git,
  editor, claude) and an exported homeModules output for use on machines
  not managed by this flake, or as an input to other flakes.

Behaviour-preserving for existing hosts: lyrathorpe-mbp and
emmathorpe-edaas evaluate to identical derivations; lyrathorpe-t400,
lyrathorpe-macpro31 and lyrathorpe-rpi5 differ only by de-duplicating a
repeated authorized_keys entry. Fixes the SSH authorized-key leak (one
user's key was applied to every account), the hardcoded default git
identity, and the hardcoded EDaaS linger setting.

hosts/EDaaS/configuration.nix

@@ -0,0 +1,78 @@
+# Edit this configuration file to define what should be installed on
+# your system. Help is available in the configuration.nix(5) man page, on
+# https://search.nixos.org/options and in the NixOS manual (`nixos-help`).
+
+# NixOS-WSL specific options are documented on the NixOS-WSL repository:
+# https://github.com/nix-community/NixOS-WSL
+
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+{
+
+  wsl = {
+    enable = true;
+    defaultUser = "emmathorpe";
+    wslConf.automount.root = "/mnt";
+    wslConf.interop.appendWindowsPath = true;
+    wslConf.interop.enabled = true;
+    wslConf.network.generateHosts = false;
+    startMenuLaunchers = true;
+    docker-desktop.enable = false;
+    extraBin = with pkgs; [
+      # Binaries for Docker Desktop wsl-distro-proxy
+      { src = "${coreutils}/bin/mkdir"; }
+      { src = "${coreutils}/bin/cat"; }
+      { src = "${coreutils}/bin/whoami"; }
+      { src = "${coreutils}/bin/ls"; }
+      { src = "${busybox}/bin/addgroup"; }
+      { src = "${su}/bin/groupadd"; }
+      { src = "${su}/bin/usermod"; }
+    ];
+  };
+
+  virtualisation.docker = {
+    enable = true;
+    enableOnBoot = true;
+    autoPrune.enable = true;
+  };
+
+  # Match the flake's nixosConfigurations attribute name so `nh os switch`
+  # (which selects by the local hostname) resolves without an explicit
+  # -H/--hostname flag. The default would otherwise be the stock NixOS "nixos".
+  networking.hostName = "emmathorpe-edaas";
+
+  networking.resolvconf.enable = false;
+
+  # Drop the systemd-ssh-proxy Include from the generated /etc/ssh/ssh_config.
+  # The NixOS-WSL store is a read-only VHD whose files are owned by nobody
+  # (65534), not root. OpenSSH permission-checks Include'd config files and
+  # rejects any not owned by root or the caller, so the default include fails
+  # with "Bad owner or permissions" and breaks ssh/git for every command. The
+  # proxy plugin only matters for `ssh unix/…` / `vsock` to local machined VMs,
+  # which WSL does not use.
+  programs.ssh.systemd-ssh-proxy.enable = false;
+
+  ## patch the script
+  systemd.services.docker-desktop-proxy.script = lib.mkForce ''${config.wsl.wslConf.automount.root}/wsl/docker-desktop/docker-desktop-user-distro proxy --docker-desktop-root ${config.wsl.wslConf.automount.root}/wsl/docker-desktop "C:\Program Files\Docker\Docker\resources"'';
+
+  features.swayDesktop.enable = false;
+
+  # NOTE: this user's systemd --user lingering -- so the home-manager renovate
+  # timer fires without an open login session -- is enabled from the host table
+  # in flake.nix (users.emmathorpe.linger = true) and applied by
+  # modules/users.nix.
+
+  # programs.nix-ld is enabled for all NixOS hosts in common-nixos.nix.
+  # This value determines the NixOS release from which the default
+  # settings for stateful data, like file locations and database versions
+  # on your system were taken. It's perfectly fine and recommended to leave
+  # this value at the release version of the first install of this system.
+  # Before changing this value read the documentation for this option
+  # (e.g. man configuration.nix or on https://nixos.org/nixos/options.html).
+  system.stateVersion = "24.11"; # Did you read the comment?
+}