feat: make DDNS domain_name the effective domain across all services

- ConfigManager.get_effective_domain(): returns domain_name when DDNS
  active (pic_ngo/cloudflare/duckdns), domain otherwise. Used by all
  public-facing services so they use the real registered FQDN.
- ConfigManager.get_internal_domain(): always returns _identity.domain
  (CoreDNS zone name, dnsmasq, cell-link invites — stays internal).
- Silent migration: if domain_mode != lan and domain is generic "cell",
  auto-set to {cell_name}.local for unique CoreDNS zone naming.
- caddy_manager: fix custom_domain bug — cloudflare/http01 modes were
  reading identity.get('custom_domain') which never exists; now reads
  domain_name correctly.
- routes/config, app: expose effective_domain in GET /api/config and
  /api/status responses.
- email_manager, routes/email: use get_effective_domain() for
  OVERRIDE_HOSTNAME, POSTMASTER_ADDRESS, and new-user email defaults.
- ServiceBus.IDENTITY_CHANGED event: emitted from PUT /api/config and
  POST /api/ddns/register after identity writes; caddy_manager and
  email_manager subscribe to regenerate config automatically.
- Settings.jsx: hide Local Domain input in non-LAN modes; show
  read-only effective_domain with "managed by DDNS" badge and an
  Advanced toggle for the internal CoreDNS zone name.
- 11 new test classes covering all new helpers, event subscriptions,
  caddy/email handlers, and the custom_domain fix.

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

tests/test_caddy_manager.py

@@ -77,7 +77,7 @@ class TestGenerateCaddyfileCloudflare(unittest.TestCase):
         identity = {
             'cell_name': 'beta',
             'domain_mode': 'cloudflare',
-            'custom_domain': 'example.com',
+            'domain_name': 'example.com',
         }
         out = mgr.generate_caddyfile(identity, [])
         self.assertIn('dns cloudflare {$CF_API_TOKEN}', out)
@@ -85,6 +85,23 @@ class TestGenerateCaddyfileCloudflare(unittest.TestCase):
         self.assertIn('email {$ACME_EMAIL}', out)
         self.assertIn('acme_ca {$ACME_CA_URL}', out)
 
+    def test_caddyfile_cloudflare_uses_domain_name(self):
+        """Caddyfile must use domain_name for TLS host, not any 'custom_domain' key."""
+        mgr = _mgr()
+        identity = {
+            'cell_name': 'beta',
+            'domain_mode': 'cloudflare',
+            'domain_name': 'home.example.com',
+            'domain': 'home.local',
+        }
+        out = mgr.generate_caddyfile(identity, [])
+        self.assertIn('*.home.example.com', out)
+        self.assertIn('home.example.com', out)
+        # Must not use the internal domain for TLS
+        self.assertNotIn('*.home.local', out)
+        # 'custom_domain' must not appear literally as a key in the output
+        self.assertNotIn('custom_domain', out)
+
 
 class TestGenerateCaddyfileDuckDns(unittest.TestCase):
     def test_duckdns_has_dns_duckdns(self):
@@ -101,7 +118,7 @@ class TestGenerateCaddyfileHttp01(unittest.TestCase):
         identity = {
             'cell_name': 'delta',
             'domain_mode': 'http01',
-            'custom_domain': 'delta.noip.me',
+            'domain_name': 'delta.noip.me',
         }
         services = [
             {'name': 'calendar', 'caddy_route':
@@ -224,5 +241,37 @@ class TestCertStatus(unittest.TestCase):
         self.assertEqual(out['days_remaining'], 84)
 
 
+class TestCaddyManagerIdentityChangedSubscription(unittest.TestCase):
+    def test_subscribes_to_identity_changed_on_init(self):
+        """When service_bus is provided, CaddyManager subscribes to IDENTITY_CHANGED."""
+        from service_bus import EventType
+        mock_bus = MagicMock()
+        mgr = CaddyManager(config_manager=MagicMock(), service_bus=mock_bus)
+        mock_bus.subscribe_to_event.assert_called_once_with(
+            EventType.IDENTITY_CHANGED, mgr._on_identity_changed
+        )
+
+    def test_no_subscription_without_service_bus(self):
+        """When service_bus is omitted, no subscription is attempted."""
+        mock_bus = MagicMock()
+        CaddyManager(config_manager=MagicMock())
+        mock_bus.subscribe_to_event.assert_not_called()
+
+    def test_on_identity_changed_calls_regenerate_with_installed(self):
+        """_on_identity_changed calls regenerate_with_installed([])."""
+        mgr = _mgr()
+        with patch.object(mgr, 'regenerate_with_installed', return_value=True) as mock_regen:
+            event = MagicMock()
+            mgr._on_identity_changed(event)
+            mock_regen.assert_called_once_with([])
+
+    def test_on_identity_changed_swallows_exceptions(self):
+        """_on_identity_changed must not propagate exceptions."""
+        mgr = _mgr()
+        with patch.object(mgr, 'regenerate_with_installed', side_effect=Exception('boom')):
+            event = MagicMock()
+            mgr._on_identity_changed(event)  # must not raise
+
+
 if __name__ == '__main__':
     unittest.main()