feat(data): per-list base branch, preserved by every config writer

src/ClaudeDo.Data/Migrations/20261001083902_AddListBaseBranch.cs

@@ -0,0 +1,28 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace ClaudeDo.Data.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddListBaseBranch : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<string>(
+                name: "base_branch",
+                table: "list_config",
+                type: "TEXT",
+                nullable: true);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "base_branch",
+                table: "list_config");
+        }
+    }
+}

src/ClaudeDo.Data/Migrations/ClaudeDoDbContextModelSnapshot.cs

@@ -268,6 +268,10 @@ namespace ClaudeDo.Data.Migrations
                         .HasColumnType("TEXT")
                         .HasColumnName("agent_path");
 
+                    b.Property<string>("BaseBranch")
+                        .HasColumnType("TEXT")
+                        .HasColumnName("base_branch");
+
                     b.Property<int?>("MaxTurns")
                         .HasColumnType("INTEGER")
                         .HasColumnName("max_turns");