Address remaining review feedback

- Use ParseIssueFilterStateIsClosed for ListProjects state parsing
- Add SortTypeProjectColumnSorting const, replace magic string
- Use GetIssueByRepoID and dedupe Add/Remove issue handlers
- Migrate Column.Sorting from int8 to int (drops 127-column limit, allows
  the API to expose a normal int without truncation)
- Introduce project_service.UpdateProject with optional.Option fields,
  use it from the API EditProject handler

Co-Authored-By: Claude (Opus 4.7) <noreply@anthropic.com>

services/convert/project.go

@@ -55,7 +55,7 @@ func ToProjectColumn(ctx context.Context, column *project_model.Column) *api.Pro
 		ID:        column.ID,
 		Title:     column.Title,
 		Default:   column.Default,
-		Sorting:   int(column.Sorting),
+		Sorting:   column.Sorting,
 		Color:     column.Color,
 		ProjectID: column.ProjectID,
 		CreatorID: column.CreatorID,