feat(data): add usage gate thresholds and task run model column

Adds AppSettings.UsageGateFiveHourPct/UsageGateSevenDayPct (defaults
80/90, clamped 0..100 in UpdateAsync) and a nullable TaskRunEntity.Model
column, laying the data foundation for the usage monitor. No worker/UI
changes.

src/ClaudeDo.Data/Configuration/TaskRunEntityConfiguration.cs

@@ -27,6 +27,7 @@ public class TaskRunEntityConfiguration : IEntityTypeConfiguration<TaskRunEntity
         builder.Property(r => r.LogPath).HasColumnName("log_path");
         builder.Property(r => r.StartedAt).HasColumnName("started_at");
         builder.Property(r => r.FinishedAt).HasColumnName("finished_at");
+        builder.Property(r => r.Model).HasColumnName("model");
 
         builder.HasOne(r => r.Task)
             .WithMany(t => t.Runs)