mailu: full nox module — client, tools and events (ADR 0044/0046)

Email server. Users/aliases/domains over the admin REST API, mail read via
doveadm in the imap container; ten tools. Emits user/alias created/deleted by
polling and diffing the admin API, so a change in the web admin is announced
as readily as one via a tool. Consumes nothing — deliberately, since mutating
mail accounts off another module's event could silently lose mail. Typechecks
against the sdk; manifest parses.

Claude-Session: https://claude.ai/code/session_01LrgweAeERJYBg88c5cKDzF

modules/mailu/module.json

@@ -4,6 +4,12 @@
   "capabilities": [
     "container-runtime"
   ],
+  "emits": [
+    "module.mailu.user.created",
+    "module.mailu.user.deleted",
+    "module.mailu.alias.created",
+    "module.mailu.alias.deleted"
+  ],
   "listens": [
     {
       "port": 25,
@@ -43,7 +49,8 @@
   "own-secrets": {
     "secret-key": "/var/lib/mailu/secret-key.secret",
     "database": "/var/lib/mailu/database.secret",
-    "admin": "/var/lib/mailu/admin.secret"
+    "admin": "/var/lib/mailu/admin.secret",
+    "broker": "/var/lib/mailu/broker"
   },
   "resources": [
     {