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.Application.Tests/Configs/Revoke/RevokeVpnConfigCommandHandlerTests.cs

@@ -85,6 +85,54 @@ public class RevokeVpnConfigCommandHandlerTests
             );
     }
 
+    [Fact]
+    public async Task Handle_WhenInboundIsUnavailable_RevokesLocallyWithoutCallingGateway()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var userId = Guid.NewGuid();
+
+        var node = Node.Register(
+            "node-1",
+            new Uri("https://node1.example.com"),
+            new NodeCredentials("admin", "protected"),
+            null
+        );
+        var inbound = Inbound.FromRemote(node.Id, "1", VpnProtocol.Vless, "remark", 443);
+        inbound.MarkUnavailable();
+        var config = VpnConfig.Create(userId, inbound.Id, VpnProtocol.Vless, null);
+        config.AssignRemoteClient("external-id");
+
+        dbContext.Nodes.Add(node);
+        dbContext.Inbounds.Add(inbound);
+        dbContext.VpnConfigs.Add(config);
+        await dbContext.SaveChangesAsync(CancellationToken.None);
+
+        var handler = new RevokeVpnConfigCommandHandler(
+            dbContext,
+            _gateway,
+            _notifier,
+            FakeCurrentUser.Authenticated(userId),
+            _logger
+        );
+
+        var result = await handler.Handle(
+            new RevokeVpnConfigCommand(config.Id),
+            CancellationToken.None
+        );
+
+        Assert.True(result.IsSuccess);
+        Assert.Equal(ConfigStatus.Revoked, config.Status);
+        await _gateway
+            .DidNotReceive()
+            .RemoveClientAsync(
+                Arg.Any<Node>(),
+                Arg.Any<string>(),
+                Arg.Any<string>(),
+                Arg.Any<VpnProtocol>(),
+                Arg.Any<CancellationToken>()
+            );
+    }
+
     [Fact]
     public async Task Handle_WhenAlreadyRevoked_IsIdempotentAndDoesNotCallGateway()
     {