feat: Improve document management with Save/Save As and keyboard shortcuts

- Track file path after save/load so Save doesn't prompt again
- Add Save As (Ctrl+Shift+S) to always prompt for location
- Update window title to show current filename
- Generate incremental default filenames (CutList_1.json, etc.)
- Add keyboard shortcuts: Ctrl+S (Save), Ctrl+O (Open), Ctrl+N (New)
- Enter key in items grid moves to Length column on next row

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CutList/Forms/MainForm.cs

@@ -9,6 +9,7 @@ namespace CutList.Forms
     public partial class MainForm : Form, IMainView
     {
         private static readonly Random random = new Random();
+        private const string BaseTitle = "Cut List";
 
         private BindingList<PartInputItem> parts;
         private BindingList<BinInputItem> bins;
@@ -32,9 +33,13 @@ namespace CutList.Forms
             binInputItemBindingSource.DataSource = bins;
             binInputItemBindingSource.ListChanged += BinInputItemBindingSource_ListChanged;
 
+
             toolbox = new Toolbox();
             cutMethodComboBox.DataSource = toolbox.Tools;
 
+            // Enable keyboard shortcuts
+            KeyPreview = true;
+
 #if DEBUG
             loadExampleDataButton.Visible = true;
 #else
@@ -140,6 +145,13 @@ namespace CutList.Forms
             LoadDocumentData(new List<PartInputItem>(), new List<BinInputItem>());
         }
 
+        public void UpdateWindowTitle(string? fileName)
+        {
+            Text = string.IsNullOrEmpty(fileName)
+                ? BaseTitle
+                : $"{fileName} - {BaseTitle}";
+        }
+
         // Event handler delegates to presenter
         private void Open()
         {
@@ -164,6 +176,61 @@ namespace CutList.Forms
             presenter.SaveDocument();
         }
 
+        private void SaveAs()
+        {
+            FlushPendingEdits();
+            presenter.SaveDocumentAs();
+        }
+
+        protected override void OnKeyDown(KeyEventArgs e)
+        {
+            base.OnKeyDown(e);
+
+            if (e.Control && e.Shift && e.KeyCode == Keys.S)
+            {
+                SaveAs();
+                e.Handled = true;
+            }
+            else if (e.Control && e.KeyCode == Keys.S)
+            {
+                Save();
+                e.Handled = true;
+            }
+            else if (e.Control && e.KeyCode == Keys.O)
+            {
+                Open();
+                e.Handled = true;
+            }
+            else if (e.Control && e.KeyCode == Keys.N)
+            {
+                presenter.NewDocument();
+                e.Handled = true;
+            }
+        }
+
+        protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
+        {
+            // Handle Enter key in items DataGridView to move to Length column
+            if (keyData == Keys.Enter && dataGridView1.CurrentCell != null &&
+                (dataGridView1.ContainsFocus || dataGridView1.IsCurrentCellInEditMode))
+            {
+                dataGridView1.EndEdit();
+
+                int currentRow = dataGridView1.CurrentCell.RowIndex;
+                int nextRow = currentRow + 1;
+                int lengthColumnIndex = lengthDataGridViewTextBoxColumn.Index;
+
+                if (nextRow < dataGridView1.RowCount)
+                {
+                    dataGridView1.CurrentCell = dataGridView1[lengthColumnIndex, nextRow];
+                    dataGridView1.BeginEdit(true);
+                    return true; // Handled
+                }
+            }
+
+            return base.ProcessCmdKey(ref msg, keyData);
+        }
+
         private void Run()
         {
             FlushPendingEdits();
@@ -281,6 +348,7 @@ namespace CutList.Forms
                 dataGridView1.Refresh();
         }
 
+
         private void dataGridView1_DataError(object sender, DataGridViewDataErrorEventArgs e)
         {
             dataGridView1.Rows[e.RowIndex].ErrorText = e.Exception.InnerException?.Message;

CutList/Presenters/IMainView.cs

@@ -88,5 +88,11 @@ namespace CutList.Presenters
         /// Clears all data in the view.
         /// </summary>
         void ClearData();
+
+        /// <summary>
+        /// Updates the window title to reflect the current document state.
+        /// </summary>
+        /// <param name="fileName">The file name to display, or null for a new document</param>
+        void UpdateWindowTitle(string? fileName);
     }
 }

CutList/Presenters/MainFormPresenter.cs

@@ -13,6 +13,7 @@ namespace CutList.Presenters
         private readonly CutListService _cutListService;
         private readonly DocumentService _documentService;
         private Document _currentDocument;
+        private int _documentCounter = 0;
 
         public MainFormPresenter(IMainView view, CutListService cutListService, DocumentService documentService)
         {
@@ -40,11 +41,13 @@ namespace CutList.Presenters
 
             _currentDocument = loadResult.Value;
             _view.LoadDocumentData(_currentDocument.PartsToNest, _currentDocument.StockBins);
+            _view.UpdateWindowTitle(Path.GetFileName(filePath));
             UpdateRunButtonState();
         }
 
         /// <summary>
-        /// Handles the "Save" operation to save the current document to file.
+        /// Handles the "Save" operation. If the document has a known path, saves directly.
+        /// Otherwise, prompts for a file location (same as Save As).
         /// </summary>
         public void SaveDocument()
         {
@@ -57,19 +60,59 @@ namespace CutList.Presenters
                 return;
             }
 
-            var defaultFileName = _currentDocument.LastFilePath == null
-                ? "NewDocument.json"
+            // If we have a known path, save directly without prompting
+            if (!string.IsNullOrEmpty(_currentDocument.LastFilePath))
+            {
+                SaveToPath(_currentDocument.LastFilePath);
+                return;
+            }
+
+            // No known path - prompt for location (same as Save As)
+            SaveDocumentAs();
+        }
+
+        /// <summary>
+        /// Handles the "Save As" operation. Always prompts for a file location.
+        /// </summary>
+        public void SaveDocumentAs()
+        {
+            SyncDocumentFromView();
+
+            var validationResult = _documentService.Validate(_currentDocument);
+            if (validationResult.IsFailure)
+            {
+                _view.ShowWarning(validationResult.Error);
+                return;
+            }
+
+            var defaultFileName = string.IsNullOrEmpty(_currentDocument.LastFilePath)
+                ? GenerateDefaultFileName()
                 : Path.GetFileName(_currentDocument.LastFilePath);
 
             if (!_view.PromptSaveFile("Json File|*.json", defaultFileName, out string filePath))
                 return;
 
+            SaveToPath(filePath);
+        }
+
+        private void SaveToPath(string filePath)
+        {
             var saveResult = _documentService.Save(_currentDocument, filePath);
 
             if (saveResult.IsFailure)
             {
                 _view.ShowError(saveResult.Error);
+                return;
             }
+
+            _currentDocument.LastFilePath = filePath;
+            _view.UpdateWindowTitle(Path.GetFileName(filePath));
+        }
+
+        private string GenerateDefaultFileName()
+        {
+            _documentCounter++;
+            return $"CutList_{_documentCounter}.json";
         }
 
         /// <summary>
@@ -100,6 +143,7 @@ namespace CutList.Presenters
         {
             _currentDocument = new Document();
             _view.ClearData();
+            _view.UpdateWindowTitle(null);
             UpdateRunButtonState();
         }
 

CutList/Services/DocumentService.cs

@@ -41,6 +41,7 @@ namespace CutList.Services
             {
                 var json = File.ReadAllText(filePath);
                 var document = JsonConvert.DeserializeObject<Document>(json);
+                document.LastFilePath = filePath;
                 return Result<Document>.Success(document);
             }
             catch (Exception ex)