fix: all service pages use live domain; cell_name/domain propagate to DNS; /api/status reads stored identity

Changes:
- ConfigContext.jsx: React context that loads /api/config once; exposes domain,
  cell_name, refresh() — wraps entire app in App.jsx
- Email/Calendar/Files pages: replace hardcoded 'mail.cell', 'calendar.cell',
  'files.cell', 'webdav.cell' with domain from ConfigContext; hostname updates
  immediately after Settings save (refreshConfig() called on save)
- /api/status: cell_name and domain now read from stored _identity in config_manager,
  not hardcoded 'personal-internet-cell' / 'cell.local'
- network_manager.apply_cell_name(old, new): updates hostname A-record in primary
  zone file and reloads CoreDNS; called from PUT /api/config when cell_name changes
- Old identity captured before save so apply_cell_name gets the correct old value
- Settings EmailForm: smtp/imap ports are read-only with note (docker-compose.yml level)
- Settings FilesForm: port is read-only with note (Caddy proxies on 80 externally)
- Settings CalendarForm: port labeled "Internal port; clients use 80 via Caddy"

Tests added:
- test_apply_cell_name_renames_host_record
- test_apply_cell_name_noop_when_same

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

tests/test_config_manager.py

@@ -335,6 +335,51 @@ class TestNetworkManagerApply(unittest.TestCase):
             "Corefile must not keep old 'cell' zone block")
 
 
+class TestNetworkManagerApplyCellName(unittest.TestCase):
+    """apply_cell_name updates the DNS zone hostname record."""
+
+    def setUp(self):
+        self.test_dir = tempfile.mkdtemp()
+        self.data_dir = os.path.join(self.test_dir, 'data')
+        self.config_dir = os.path.join(self.test_dir, 'config')
+        os.makedirs(os.path.join(self.data_dir, 'dns'), exist_ok=True)
+        os.makedirs(os.path.join(self.config_dir, 'dhcp'), exist_ok=True)
+        os.makedirs(os.path.join(self.config_dir, 'ntp'), exist_ok=True)
+        with open(os.path.join(self.config_dir, 'dhcp', 'dnsmasq.conf'), 'w') as f:
+            f.write('domain=cell\n')
+        with open(os.path.join(self.config_dir, 'ntp', 'chrony.conf'), 'w') as f:
+            f.write('server pool.ntp.org iburst\n')
+        # Create a zone file with old cell name
+        with open(os.path.join(self.data_dir, 'dns', 'cell.zone'), 'w') as f:
+            f.write('$ORIGIN cell.\n$TTL 300\n'
+                    '@ IN SOA ns1.cell. admin.cell. 2024010101 3600 900 604800 300\n'
+                    'ns1      IN A 172.20.0.3\n'
+                    'mycell   IN A 172.20.0.2\n'
+                    '@        IN A 172.20.0.2\n')
+        sys.path.insert(0, str(Path(__file__).parent.parent / 'api'))
+        from network_manager import NetworkManager
+        self.nm = NetworkManager(self.data_dir, self.config_dir)
+
+    def tearDown(self):
+        shutil.rmtree(self.test_dir)
+
+    @patch('subprocess.run')
+    def test_apply_cell_name_renames_host_record(self, mock_run):
+        mock_run.return_value = MagicMock(returncode=0)
+        result = self.nm.apply_cell_name('mycell', 'newcell')
+        zone = open(os.path.join(self.data_dir, 'dns', 'cell.zone')).read()
+        self.assertIn('newcell   IN A 172.20.0.2', zone)
+        self.assertNotIn('mycell   IN A', zone)
+        self.assertIn('cell-dns', ' '.join(result['restarted']))
+
+    @patch('subprocess.run')
+    def test_apply_cell_name_noop_when_same(self, mock_run):
+        mock_run.return_value = MagicMock(returncode=0)
+        result = self.nm.apply_cell_name('mycell', 'mycell')
+        self.assertEqual(result['restarted'], [])
+        mock_run.assert_not_called()
+
+
 class TestEmailManagerApply(unittest.TestCase):
     """Test email_manager.apply_config writes mailserver.env correctly."""