feat(data): add ClaudeDoDbContext with Fluent API configurations

src/ClaudeDo.Data/Configuration/SubtaskEntityConfiguration.cs

@@ -0,0 +1,28 @@
+using ClaudeDo.Data.Models;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace ClaudeDo.Data.Configuration;
+
+public class SubtaskEntityConfiguration : IEntityTypeConfiguration<SubtaskEntity>
+{
+    public void Configure(EntityTypeBuilder<SubtaskEntity> builder)
+    {
+        builder.ToTable("subtasks");
+
+        builder.HasKey(s => s.Id);
+        builder.Property(s => s.Id).HasColumnName("id");
+        builder.Property(s => s.TaskId).HasColumnName("task_id").IsRequired();
+        builder.Property(s => s.Title).HasColumnName("title").IsRequired();
+        builder.Property(s => s.Completed).HasColumnName("completed").IsRequired().HasDefaultValue(false);
+        builder.Property(s => s.OrderNum).HasColumnName("order_num").IsRequired();
+        builder.Property(s => s.CreatedAt).HasColumnName("created_at").IsRequired();
+
+        builder.HasOne(s => s.Task)
+            .WithMany(t => t.Subtasks)
+            .HasForeignKey(s => s.TaskId)
+            .OnDelete(DeleteBehavior.Cascade);
+
+        builder.HasIndex(s => s.TaskId).HasDatabaseName("idx_subtasks_task_id");
+    }
+}