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/hub/ws/request_manager.go

@@ -45,7 +45,15 @@ func NewRequestManager(conn *gws.Conn) *RequestManager {
 func (rm *RequestManager) SendRequest(ctx context.Context, action common.WebSocketAction, data any) (*PendingRequest, error) {
 	reqID := RequestID(rm.nextID.Add(1))
 
-	reqCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	// Respect any caller-provided deadline. If none is set, apply a reasonable default
+	// so pending requests don't live forever if the agent never responds.
+	reqCtx := ctx
+	var cancel context.CancelFunc
+	if _, hasDeadline := ctx.Deadline(); hasDeadline {
+		reqCtx, cancel = context.WithCancel(ctx)
+	} else {
+		reqCtx, cancel = context.WithTimeout(ctx, 5*time.Second)
+	}
 
 	req := &PendingRequest{
 		ID:         reqID,
@@ -100,6 +108,11 @@ func (rm *RequestManager) handleResponse(message *gws.Message) {
 		return
 	}
 
+	if response.Id == nil {
+		rm.routeLegacyResponse(message)
+		return
+	}
+
 	reqID := RequestID(*response.Id)
 
 	rm.RLock()