fix: fall back to cell effective domain when email service domain not configured

When the email store service is installed but no explicit domain has been
set in its config, _provision_email now falls back to
config_manager.get_effective_domain() so peer account creation works
immediately without requiring a separate config step.

Also threads config_manager into AccountManager.__init__ (optional kwarg,
no existing callers break) so the fallback is available without a global
import.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/account_manager.py

@@ -52,15 +52,17 @@ _HTTP_TIMEOUT = 10
 
 class AccountManager:
 
-    def __init__(self, service_registry, data_dir: str, **managers):
+    def __init__(self, service_registry, data_dir: str, config_manager=None, **managers):
         """
         service_registry — ServiceRegistry instance
         data_dir         — host data directory (data/peer_service_credentials.json lives here)
+        config_manager   — ConfigManager instance (used to resolve fallback email domain)
         **managers       — named manager instances: email_manager=..., calendar_manager=...,
                            file_manager=...
         """
         self._registry = service_registry
         self._creds_path = Path(data_dir) / 'peer_service_credentials.json'
+        self._config_manager = config_manager
         self._managers = managers
         self._lock = threading.Lock()
 
@@ -88,6 +90,8 @@ class AccountManager:
 
     def _provision_email(self, manager, svc: Dict, peer_username: str, password: str) -> bool:
         domain = (svc.get('config') or {}).get('domain', '')
+        if not domain and self._config_manager is not None:
+            domain = self._config_manager.get_effective_domain() or ''
         if not domain:
             raise ValueError("Email service has no 'domain' configured")
         return manager.create_email_user(peer_username, domain, password)

api/managers.py

@@ -80,6 +80,7 @@ service_composer = ServiceComposer(config_manager=config_manager, data_dir=DATA_
 account_manager  = AccountManager(
     service_registry=service_registry,
     data_dir=DATA_DIR,
+    config_manager=config_manager,
     email_manager=email_manager,
     calendar_manager=calendar_manager,
     file_manager=file_manager,