Add IsAvailable property to Inbound and update related logic

- Introduced a new boolean property, `IsAvailable`, to the `Inbound` entity to track the availability status of inbounds based on synchronization results.
- Updated the `SyncNodeCommandHandler` to mark inbounds as unavailable if they are not present in the latest synchronization but have existing configurations, preventing their deletion.
- Enhanced the `MarkUnavailable` method to set both `IsAvailable` and `IsPublished` to false, reflecting the new status accurately.
- Modified the frontend components to display the availability status of inbounds, ensuring users are informed of their current state.
- Updated tests to cover the new behavior regarding inbound availability and its impact on revocation processes.

backend/tests/PnvPanel.Domain.Tests/Inbounds/InboundTests.cs

@@ -60,4 +60,24 @@ public class InboundTests
         Assert.False(inbound.IsPublished);
         Assert.Contains(roleId, inbound.AllowedRoleIds);
     }
+
+    [Fact]
+    public void FromRemote_CreatesAvailableInbound()
+    {
+        var inbound = Inbound.FromRemote(Guid.NewGuid(), "12", VpnProtocol.Vless, "Germany", 443);
+
+        Assert.True(inbound.IsAvailable);
+    }
+
+    [Fact]
+    public void MarkUnavailable_SetsIsAvailableAndIsPublishedFalse()
+    {
+        var inbound = Inbound.FromRemote(Guid.NewGuid(), "12", VpnProtocol.Vless, "Germany", 443);
+        inbound.Publish("Germany", [Guid.NewGuid()]);
+
+        inbound.MarkUnavailable();
+
+        Assert.False(inbound.IsAvailable);
+        Assert.False(inbound.IsPublished);
+    }
 }