feat(data): list_folders table plus lists.folder_id

Sidebar folders get their own table rather than a flag on lists, so the
places that enumerate lists (MCP tools, move-to-list, queue picker, repo
import) need no folder filtering. ON DELETE SET NULL keeps a folder's
lists alive when the folder goes.

src/ClaudeDo.Data/Configuration/ListFolderEntityConfiguration.cs

@@ -0,0 +1,23 @@
+using ClaudeDo.Data.Models;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace ClaudeDo.Data.Configuration;
+
+public class ListFolderEntityConfiguration : IEntityTypeConfiguration<ListFolderEntity>
+{
+    public void Configure(EntityTypeBuilder<ListFolderEntity> builder)
+    {
+        builder.ToTable("list_folders");
+
+        builder.HasKey(f => f.Id);
+        builder.Property(f => f.Id).HasColumnName("id");
+        builder.Property(f => f.Name).HasColumnName("name").IsRequired();
+        builder.Property(f => f.CreatedAt).HasColumnName("created_at").IsRequired();
+        builder.Property(f => f.Icon).HasColumnName("icon");
+        builder.Property(f => f.SortOrder).HasColumnName("sort_order").IsRequired().HasDefaultValue(0);
+        builder.Property(f => f.IsCollapsed).HasColumnName("is_collapsed").IsRequired().HasDefaultValue(false);
+
+        builder.HasIndex(f => f.SortOrder).HasDatabaseName("idx_list_folders_sort");
+    }
+}