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.

home/claude/memory/jira_tooling.md

@@ -0,0 +1,21 @@
+---
+name: jira-tooling
+description: Jira MCP tool quirks — comment markdown, transitions, link direction, WSP transition IDs
+metadata:
+  type: feedback
+---
+
+**Comment markup:** `addCommentToJiraIssue` `commentBody` renders as Markdown — use `###` headings, `**bold**`, backtick `code`, `1.` / `-` lists. Do NOT use wiki markup (`h3.`, `{{code}}`, `_italic_`, `#` numbered) — it renders literally.
+
+**Transitions:** `transitionJiraIssue` may fail if the issue lacks an assignee. Set assignee first via `editJiraIssue` when a transition errors on assignee requirement.
+
+**Issue link direction:** For `createIssueLink`, "X is blocked by Y" means `inwardIssue=Y` (the blocker), `outwardIssue=X` (the blocked), `type.name="Blocks"`. Inward = the side the link points _from_; outward = the side it points _to_.
+
+**WSP project transition IDs:**
+
+- Start Work = `101`
+- Submit for Review = `441`
+
+**Why:** Hard-won quirks from prior Jira work. Cuts trial-and-error.
+
+**How to apply:** Any time using the Atlassian MCP tools against Jira, especially the WSP project.