feat: P0-2b implement ControlHost via xcecli_hostctrl + fix allFlag race

- backend/clib.go: Replace ControlHost stub with real implementation
  using xcecli_hostctrl, following the same pattern as ControlQueue
- controllers/hosts.go: Remove package-level allFlag variable;
  preCheckHostControlRequest now returns (bool, error) so the allFlag
  is a local value in the caller, eliminating the data race
- controllers/queues.go: Same fix for preCheckQueueControlRequest
- Add unit tests for both preCheck functions verifying return values,
  error cases, and concurrent safety
- Add compile-time verification test for ControlHost stub signature

src/frontend/apiserver/controllers/queue_control_test.go

@@ -0,0 +1,139 @@
+package controllers
+
+import (
+	"apiserver/models"
+	"apiserver/store"
+	"apiserver/utils"
+	"sync"
+	"testing"
+
+	"go.uber.org/zap"
+)
+
+func resetQueueControlState() {
+	store.InitStores()
+	utils.Log = zap.NewNop()
+}
+
+// TestPreCheckQueueControlRequest_AllFlag verifies that when queue_name is
+// ["all"], the returned bool is true.
+func TestPreCheckQueueControlRequest_AllFlag(t *testing.T) {
+	resetQueueControlState()
+
+	req := &models.QueueControlRequest{
+		ControlAction: "close",
+		QueueName:     []string{"all"},
+	}
+
+	allFlag, err := preCheckQueueControlRequest(req)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !allFlag {
+		t.Error("expected allFlag=true when queue_name is [\"all\"]")
+	}
+}
+
+// TestPreCheckQueueControlRequest_NotAll verifies that when queue_name is a
+// specific queue, the returned bool is false.
+func TestPreCheckQueueControlRequest_NotAll(t *testing.T) {
+	resetQueueControlState()
+
+	req := &models.QueueControlRequest{
+		ControlAction: "open",
+		QueueName:     []string{"normal"},
+	}
+
+	allFlag, err := preCheckQueueControlRequest(req)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if allFlag {
+		t.Error("expected allFlag=false when queue_name is [\"normal\"]")
+	}
+}
+
+// TestPreCheckQueueControlRequest_NoRace verifies that concurrent calls to
+// preCheckQueueControlRequest do not share state via a package-level variable.
+func TestPreCheckQueueControlRequest_NoRace(t *testing.T) {
+	t.Parallel()
+	resetQueueControlState()
+
+	var wg sync.WaitGroup
+	const goroutines = 50
+
+	results := make([]bool, goroutines)
+	errors := make([]error, goroutines)
+
+	for i := 0; i < goroutines; i++ {
+		wg.Add(1)
+		go func(idx int) {
+			defer wg.Done()
+			var req models.QueueControlRequest
+			if idx%2 == 0 {
+				req = models.QueueControlRequest{
+					ControlAction: "close",
+					QueueName:     []string{"all"},
+				}
+			} else {
+				req = models.QueueControlRequest{
+					ControlAction: "open",
+					QueueName:     []string{"normal"},
+				}
+			}
+			results[idx], errors[idx] = preCheckQueueControlRequest(&req)
+		}(i)
+	}
+	wg.Wait()
+
+	for i := 0; i < goroutines; i++ {
+		if errors[i] != nil {
+			t.Errorf("goroutine %d: unexpected error: %v", i, errors[i])
+			continue
+		}
+		if i%2 == 0 && !results[i] {
+			t.Errorf("goroutine %d: expected allFlag=true for [\"all\"]", i)
+		}
+		if i%2 != 0 && results[i] {
+			t.Errorf("goroutine %d: expected allFlag=false for [\"normal\"]", i)
+		}
+	}
+}
+
+// TestPreCheckQueueControlRequest_InvalidAction verifies that an unsupported
+// action returns an error.
+func TestPreCheckQueueControlRequest_InvalidAction(t *testing.T) {
+	resetQueueControlState()
+
+	req := &models.QueueControlRequest{
+		ControlAction: "invalid_action",
+		QueueName:     []string{"normal"},
+	}
+
+	_, err := preCheckQueueControlRequest(req)
+	if err == nil {
+		t.Error("expected error for invalid action, got nil")
+	}
+}
+
+// TestPreCheckQueueControlRequest_CommentTooLong verifies that a comment
+// exceeding 512 characters returns an error.
+func TestPreCheckQueueControlRequest_CommentTooLong(t *testing.T) {
+	resetQueueControlState()
+
+	longComment := make([]byte, 513)
+	for i := range longComment {
+		longComment[i] = 'a'
+	}
+
+	req := &models.QueueControlRequest{
+		ControlAction: "close",
+		QueueName:     []string{"normal"},
+		Comment:       string(longComment),
+	}
+
+	_, err := preCheckQueueControlRequest(req)
+	if err == nil {
+		t.Error("expected error for comment exceeding 512 chars, got nil")
+	}
+}