Clean up and fix service integration

- Remove redundant Document initialization in MainForm
- Update CutListService to use SetBins method for MultiBinEngine
- Update MultiBinEngine instantiation to follow proper initialization pattern
- Ensure spacing is set after bins are configured

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

CutList/Forms/MainForm.cs

@@ -41,8 +41,6 @@ namespace CutList.Forms
             toolbox = new Toolbox();
             cutMethodComboBox.DataSource = toolbox.Tools;
 
-            currentDocument = new Document();
-
 #if DEBUG
             loadExampleDataButton.Visible = true;
 #else

CutList/Services/CutListService.cs

@@ -27,11 +27,9 @@ namespace CutList.Services
                 var multiBins = ConvertToMultiBins(stockBins);
                 var binItems = ConvertToBinItems(parts);
 
-                var engine = new MultiBinEngine
-                {
-                    Spacing = cuttingTool.Kerf,
-                    Bins = multiBins
-                };
+                var engine = new MultiBinEngine();
+                engine.SetBins(multiBins);
+                engine.Spacing = cuttingTool.Kerf;
 
                 var packResult = engine.Pack(binItems);
                 return Result<SawCut.Nesting.Result>.Success(packResult);