Go: Add admin server status checking (#13571)

### What problem does this PR solve?

RAGFlow server isn't available when admin server isn't connected.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

internal/server/local/admin_status.go

@@ -0,0 +1,79 @@
+//
+//  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+//
+
+package local
+
+import (
+	"sync"
+)
+
+// AdminStatus represents the admin status
+// 0 = valid, 1 = invalid
+type AdminStatus struct {
+	Status int    `json:"status"` // 0 = available, 1 = not available
+	Reason string `json:"reason"` // reason for invalid status
+}
+
+var (
+	adminStatus     *AdminStatus
+	adminStatusMu   sync.RWMutex
+	adminStatusOnce sync.Once
+)
+
+// InitAdminStatus initializes the global admin status
+// status: 0 = valid, 1 = invalid (default)
+func InitAdminStatus(status int, reason string) {
+	adminStatusOnce.Do(func() {
+		adminStatus = &AdminStatus{
+			Status: status,
+			Reason: reason,
+		}
+	})
+}
+
+// GetAdminStatus returns the current admin status
+func GetAdminStatus() AdminStatus {
+	adminStatusMu.RLock()
+	defer adminStatusMu.RUnlock()
+	if adminStatus == nil {
+		return AdminStatus{Status: 1, Reason: "not initialized"}
+	}
+	return AdminStatus{
+		Status: adminStatus.Status,
+		Reason: adminStatus.Reason,
+	}
+}
+
+// SetAdminStatus updates the admin status
+func SetAdminStatus(status int, reason string) {
+	adminStatusMu.Lock()
+	defer adminStatusMu.Unlock()
+	if adminStatus == nil {
+		adminStatus = &AdminStatus{}
+	}
+	adminStatus.Status = status
+	adminStatus.Reason = reason
+}
+
+// IsAdminAvailable returns true if admin is valid (Status == 0)
+func IsAdminAvailable() bool {
+	adminStatusMu.RLock()
+	defer adminStatusMu.RUnlock()
+	if adminStatus == nil {
+		return false
+	}
+	return adminStatus.Status == 0
+}