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.

users/emmathorpe/work.nix

@@ -0,0 +1,69 @@
+# Home-manager module for the work (EDaaS/WSL) profile: corporate work toolchain
+# packages and tmux tweaks. Imported only by the work host. The corporate git
+# identity (email + signing key) is the emmathorpe entry in the identity
+# registry (users/registry.nix), applied by the shared home/git.nix.
+{ pkgs, lib, ... }:
+
+{
+  # Host-scoped extras for this machine only (the EDaaS/WSL host).
+  imports = [
+    ./renovate-review.nix # daily headless Renovate PR review (systemd user timer)
+  ];
+
+  # The work box keeps its own (corporate) ~/.ssh/config; don't let the personal
+  # programs.ssh (shell.nix) take it over. The ssh-agent below still runs.
+  programs.ssh.enable = lib.mkForce false;
+
+  home.packages = [
+    pkgs.kubectl
+    pkgs.argo-rollouts
+    pkgs.tenv
+    pkgs.kubernetes-helm
+    pkgs.azure-cli
+    pkgs.kubelogin
+    pkgs.curl
+    pkgs.notation
+    pkgs.powershell
+    pkgs.nuget
+    pkgs.gedit
+    pkgs.lens
+    pkgs.python3
+    pkgs.gnumake
+    pkgs.gcc
+    pkgs.libiconv
+    pkgs.autoconf
+    pkgs.automake
+    pkgs.pkg-config
+    pkgs.wget
+    pkgs.google-cloud-sdk
+    # Day-to-day Kubernetes / Helm / Terraform accelerators for this box.
+    pkgs.k9s # cluster TUI
+    pkgs.kubectx # kubectx + kubens (context/namespace switch)
+    pkgs.stern # multi-pod log tail
+    pkgs.dyff # semantic YAML/manifest diffs (Helm release drift)
+    pkgs.tflint # Terraform linter (catches what terraformls won't)
+    pkgs.terraform-docs # generate Terraform module docs
+    pkgs.yq-go # jq for YAML
+  ];
+  services.ssh-agent.enable = true;
+  home.shellAliases = {
+    docker = "/run/current-system/sw/bin/docker";
+  };
+  programs.tmux = {
+    extraConfig = ''
+      			set -g status-right "#(/run/current-system/sw/bin/bash $HOME/code/kube-tmux/kube.tmux 250 red black)"		
+    '';
+  };
+  programs.go = {
+    enable = true;
+  };
+
+  # LSP servers only relevant to work: C# (omnisharp) and Helm charts (helm_ls).
+  # The shared editor (home/editor.nix) carries the universal ones;
+  # these are gated to this host so the heavy omnisharp closure stays off the
+  # personal machines. Tree-sitter grammars (highlighting) remain global there.
+  programs.nixvim.plugins.lsp.servers = {
+    omnisharp.enable = true;
+    helm_ls.enable = true;
+  };
+}