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>

api/network_manager.py

@@ -422,6 +422,36 @@ class NetworkManager(BaseServiceManager):
             warnings.append(f"CoreDNS reload failed: {e}")
 
         return {'restarted': restarted, 'warnings': warnings}
+
+    def apply_cell_name(self, old_name: str, new_name: str) -> Dict[str, Any]:
+        """Update the cell hostname record in the primary DNS zone file."""
+        restarted = []
+        warnings = []
+        if not old_name or not new_name or old_name == new_name:
+            return {'restarted': restarted, 'warnings': warnings}
+        try:
+            dns_data = os.path.join(self.data_dir, 'dns')
+            if os.path.isdir(dns_data):
+                for fname in os.listdir(dns_data):
+                    if fname.endswith('.zone') and 'local' not in fname:
+                        zone_file = os.path.join(dns_data, fname)
+                        with open(zone_file) as f:
+                            content = f.read()
+                        # Replace hostname record: old_name  IN A ...
+                        import re
+                        content = re.sub(
+                            rf'^{re.escape(old_name)}(\s+IN\s+A\s+)',
+                            f'{new_name}\\1',
+                            content, flags=re.MULTILINE
+                        )
+                        with open(zone_file, 'w') as f:
+                            f.write(content)
+                        break
+            self._reload_dns_service()
+            restarted.append('cell-dns (reloaded)')
+        except Exception as e:
+            warnings.append(f"cell_name DNS update failed: {e}")
+        return {'restarted': restarted, 'warnings': warnings}
     
     def test_dns_resolution(self, domain: str) -> Dict:
         """Test DNS resolution for a domain using Python socket."""