refactor(usage): drop the transcript aggregation path in favour of TokenTracker

tests/ClaudeDo.Worker.Tests/Runner/RunUsagePersistenceTests.cs

@@ -155,10 +155,6 @@ public sealed class RunUsagePersistenceTests : IDisposable
 
     private sealed class ThrowingUsageReader : ITranscriptUsageReader
     {
-        public Task<IReadOnlyList<UsageAggregateRow>> ReadAsync(
-            DateOnly start, DateOnly end, CancellationToken ct = default) =>
-            throw new IOException("boom");
-
         public Task<SessionUsageTotals?> ReadSessionTotalsAsync(string sessionId, CancellationToken ct = default) =>
             throw new IOException("boom");
     }