refactor: unify agent communication with Transport interface

- Introduce `Transport` interface to abstract WebSocket and SSH
communication
- Add generic `Data` field to `AgentResponse` for streamlined future
endpoints
- Maintain backward compatibility with legacy hubs and agents using
typed fields
- Unify fetch operations (SMART, systemd, containers) under a single
`request` method
- Improve `RequestManager` with deadline awareness and legacy response
support
- Refactor agent response routing into dedicated `agent/response.go`
- Update version to 0.18.0-beta.2

internal/site/src/components/systems-table/systems-table-columns.tsx

@@ -287,12 +287,12 @@ export function SystemsTableColumns(viewMode: "table" | "grid"): ColumnDef<Syste
 					return null
 				}
 
-				const iconColor = pct < 10 ? "text-red-500" : pct < 25 ? "text-yellow-500" : "text-muted-foreground"
-
 				let Icon = PlugChargingIcon
+				let iconColor = "text-muted-foreground"
 
 				if (state !== BatteryState.Charging) {
 					if (pct < 25) {
+						iconColor = pct < 11 ? "text-red-500" : "text-yellow-500"
 						Icon = BatteryLowIcon
 					} else if (pct < 75) {
 						Icon = BatteryMediumIcon