refactor: remove standalone proxies, add Traefik provider with Docker labels

Standalone proxy removal:
- Delete store, API handlers, proxy manager, health monitor, validator, hints
- Delete frontend pages (proxies list, create, edit) and components (ProxyCard, ProxyForm, ProxyFilter, ProxyGroup, ValidationChecklist)
- Remove proxy routes from router, nav items, dashboard references
- Clean up SystemHealthCard to remove proxy section

Traefik provider:
- Add TraefikProvider implementing proxy.Provider via Docker labels
- ContainerLabels() returns traefik.enable, router rule, entrypoints, service port, TLS cert resolver, docker network
- ConfigureRoute() returns router name (labels handle routing at container creation)
- DeleteRoute() is no-op (container removal auto-deregisters)
- Ping() checks Traefik API health (optional)
- Wire ContainerLabels into deployer (executeDeploy + blueGreenDeploy)
- Add Traefik settings: entrypoint, cert_resolver, network, api_url
- Add traefik option to proxy provider selector in settings UI
- Show conditional Traefik config fields
- Add i18n keys (EN + RU)

internal/api/dns.go

@@ -202,12 +202,6 @@ func (s *Server) buildConsumerNameMap() map[string]string {
 		}
 	}
 
-	// Standalone proxy consumers: "standalone:id" -> domain
-	proxies, _ := s.store.ListStandaloneProxies()
-	for _, p := range proxies {
-		names["standalone:"+p.ID] = p.Domain
-	}
-
 	return names
 }
 
@@ -373,13 +367,5 @@ func (s *Server) computeExpectedFQDNs(settings store.Settings) (map[string]strin
 		}
 	}
 
-	// Standalone proxies.
-	proxies, _ := s.store.ListStandaloneProxies()
-	for _, p := range proxies {
-		if p.Domain != "" {
-			expected[p.Domain] = "standalone:" + p.ID
-		}
-	}
-
 	return expected, nil
 }