feat: Settings changes now apply to real service config files and restart containers

Each service manager now has apply_config() that writes to the actual config:
- network: dhcp_range → dnsmasq.conf (reload cell-dhcp), ntp_servers → chrony.conf
  (restart cell-ntp), domain → dnsmasq.conf domain= line
- email: domain → mailserver.env OVERRIDE_HOSTNAME + POSTMASTER_ADDRESS,
  restart cell-mail
- wireguard: port/address/private_key → wg0.conf ListenPort/Address/PrivateKey,
  restart cell-wireguard
- calendar: port → radicale config hosts=, restart cell-radicale

PUT /api/config now calls apply_config() after persisting JSON, and returns
{restarted: [...], warnings: [...]} so Settings UI can show which containers
were restarted. _restart_container() helper added to BaseServiceManager.

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

api/base_service_manager.py

@@ -68,11 +68,31 @@ class BaseServiceManager(ABC):
         """Restart service - default implementation"""
         try:
             self.logger.info(f"Restarting {self.service_name} service")
-            # Default implementation - subclasses can override
             return True
         except Exception as e:
             self.logger.error(f"Error restarting {self.service_name}: {e}")
             return False
+
+    def _restart_container(self, container_name: str) -> bool:
+        """Restart a Docker container by name."""
+        import subprocess
+        try:
+            result = subprocess.run(
+                ['docker', 'restart', container_name],
+                capture_output=True, text=True, timeout=30
+            )
+            if result.returncode == 0:
+                self.logger.info(f"Restarted container {container_name}")
+                return True
+            self.logger.error(f"Failed to restart {container_name}: {result.stderr}")
+            return False
+        except Exception as e:
+            self.logger.error(f"Error restarting container {container_name}: {e}")
+            return False
+
+    def apply_config(self, config: Dict[str, Any]) -> Dict[str, Any]:
+        """Apply config to actual service files and restart. Override in subclasses."""
+        return {'restarted': [], 'warnings': []}
     
     def get_config(self) -> Dict[str, Any]:
         """Get service configuration - default implementation"""