Fix query and API bugs: 403 for non-owners, page bounds, lifecycle filters, cover fallback, race-safe inserts, async album delete

backend/Core/Musify.Application/Contracts/IDatabase.cs

@@ -1,3 +1,4 @@
+using ErrorOr;
 using Microsoft.EntityFrameworkCore;
 using Musify.Domain.Entities;
 
@@ -38,4 +39,6 @@ public interface IDatabase
     public Task<IDatabaseTransaction> BeginTransactionAsync(System.Data.IsolationLevel isolationLevel, CancellationToken cancellationToken);
 
     public Task<int> SaveChangesAsync(CancellationToken cancellationToken);
+
+    public Task<ErrorOr<Success>> TrySaveChangesAsync(Error onUniqueViolation, CancellationToken cancellationToken);
 }

backend/Core/Musify.Application/Contracts/IStorageService.cs

@@ -2,7 +2,7 @@ namespace Musify.Application.Contracts;
 
 public interface IStorageService
 {
-    public Task<Stream> GetFileAsync(string bucket, string key, CancellationToken cancellationToken);
+    public Task<Stream?> GetFileAsync(string bucket, string key, CancellationToken cancellationToken);
 
     public Task<ObjectMetaData?> HeadObjectAsync(string bucket, string key, CancellationToken cancellationToken);