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/src/PnvPanel.Infrastructure/Persistence/Migrations/AppDbContextModelSnapshot.cs

@@ -359,6 +359,9 @@ namespace PnvPanel.Infrastructure.Persistence.Migrations
                         .HasMaxLength(100)
                         .HasColumnType("character varying(100)");
 
+                    b.Property<bool>("IsAvailable")
+                        .HasColumnType("boolean");
+
                     b.Property<bool>("IsPublished")
                         .HasColumnType("boolean");