feat(lists): selectable list/folder colors with accent-aware swatches and custom picker

tests/ClaudeDo.Data.Tests/ListFolderTests.cs

@@ -80,6 +80,31 @@ public sealed class ListFolderTests : IDisposable
         }
     }
 
+    [Fact]
+    public async Task List_color_round_trips_and_defaults_to_null()
+    {
+        await using (var ctx = Open())
+        {
+            var repo = new ListRepository(ctx);
+            await repo.AddAsync(new ListEntity { Id = "l1", Name = "Plain", CreatedAt = DateTime.UtcNow });
+            await repo.AddAsync(new ListEntity { Id = "l2", Name = "Tinted", CreatedAt = DateTime.UtcNow, Color = "Swatch3" });
+        }
+
+        await using (var ctx = Open())
+        {
+            var repo = new ListRepository(ctx);
+            Assert.Null((await ctx.Lists.AsNoTracking().FirstAsync(l => l.Id == "l1")).Color);
+            Assert.Equal("Swatch3", (await ctx.Lists.AsNoTracking().FirstAsync(l => l.Id == "l2")).Color);
+
+            var tinted = (await repo.GetByIdAsync("l2"))!;
+            tinted.Color = "#A1B2C3";
+            await repo.UpdateAsync(tinted);
+        }
+
+        await using (var ctx = Open())
+            Assert.Equal("#A1B2C3", (await ctx.Lists.AsNoTracking().FirstAsync(l => l.Id == "l2")).Color);
+    }
+
     [Fact]
     public async Task SetListFolderAsync_moves_a_list_in_and_back_out()
     {