feat(lists): assign a colour to a sidebar folder

Tints the folder name and its guide line; picked from a swatch row in the folder settings.

tests/ClaudeDo.Data.Tests/ListFolderTests.cs

@@ -67,13 +67,14 @@ public sealed class ListFolderTests : IDisposable
         }
 
         await using (var ctx = Open())
-            await new ListRepository(ctx).RenameFolderAsync("f2", "Renamed", "Star");
+            await new ListRepository(ctx).RenameFolderAsync("f2", "Renamed", "Star", "#7FA7C9");
 
         await using (var ctx = Open())
         {
             var folder = await ctx.ListFolders.AsNoTracking().FirstAsync(f => f.Id == "f2");
             Assert.Equal("Renamed", folder.Name);
             Assert.Equal("Star", folder.Icon);
+            Assert.Equal("#7FA7C9", folder.Color);
             Assert.True(folder.IsCollapsed);
             Assert.Equal(1, folder.SortOrder);
         }