Update services to use Result pattern

Refactor DocumentService and CutListService to return Result<T>
instead of throwing exceptions or using out parameters. This
removes all MessageBox calls from business logic.

DocumentService changes:
- Load() returns Result<Document> instead of Document
- Save() returns Result instead of void
- Validate() returns Result instead of bool with out parameter
- All exceptions caught and converted to Result.Failure

CutListService changes:
- Pack() returns Result<SawCut.Nesting.Result>
- Exceptions caught and converted to Result.Failure

Benefits:
- Services are now UI-agnostic (no MessageBox)
- Can be unit tested without UI dependencies
- Can be reused in console apps, web apps, etc.
- Errors are values, not exceptions
- Clear, type-safe error handling contract

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

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

CutList/Services/CutListService.cs

@@ -1,6 +1,8 @@
+using CutList.Common;
 using CutList.Models;
 using SawCut;
 using SawCut.Nesting;
+using System;
 using System.Collections.Generic;
 
 namespace CutList.Services
@@ -17,19 +19,27 @@ namespace CutList.Services
         /// <param name="parts">The parts to be nested</param>
         /// <param name="stockBins">The available stock bins</param>
         /// <param name="cuttingTool">The cutting tool to use (determines kerf/spacing)</param>
-        /// <returns>The packing result with optimized bins and unused items</returns>
+        /// <returns>Result containing the packing result with optimized bins and unused items, or error message</returns>
-        public Result Pack(List<PartInputItem> parts, List<BinInputItem> stockBins, Tool cuttingTool)
+        public Result<SawCut.Nesting.Result> Pack(List<PartInputItem> parts, List<BinInputItem> stockBins, Tool cuttingTool)
         {
-            var multiBins = ConvertToMultiBins(stockBins);
+            try
-            var binItems = ConvertToBinItems(parts);
-
-            var engine = new MultiBinEngine
             {
-                Spacing = cuttingTool.Kerf,
+                var multiBins = ConvertToMultiBins(stockBins);
-                Bins = multiBins
+                var binItems = ConvertToBinItems(parts);
-            };
 
-            return engine.Pack(binItems);
+                var engine = new MultiBinEngine
+                {
+                    Spacing = cuttingTool.Kerf,
+                    Bins = multiBins
+                };
+
+                var packResult = engine.Pack(binItems);
+                return Result<SawCut.Nesting.Result>.Success(packResult);
+            }
+            catch (Exception ex)
+            {
+                return Result<SawCut.Nesting.Result>.Failure($"Packing failed: {ex.Message}");
+            }
         }
 
         private List<MultiBin> ConvertToMultiBins(List<BinInputItem> stockBins)

CutList/Services/DocumentService.cs

@@ -1,3 +1,4 @@
+using CutList.Common;
 using CutList.Forms;
 using Newtonsoft.Json;
 using System;
@@ -16,49 +17,58 @@ namespace CutList.Services
         /// </summary>
         /// <param name="document">The document to save</param>
         /// <param name="filePath">The file path to save to</param>
-        /// <exception cref="IOException">Thrown when file cannot be saved</exception>
+        /// <returns>Result indicating success or failure with error message</returns>
-        public void Save(Document document, string filePath)
+        public Result Save(Document document, string filePath)
         {
-            var json = JsonConvert.SerializeObject(document, Formatting.Indented);
+            try
-            File.WriteAllText(filePath, json);
+            {
+                var json = JsonConvert.SerializeObject(document, Formatting.Indented);
+                File.WriteAllText(filePath, json);
+                return Result.Success();
+            }
+            catch (Exception ex)
+            {
+                return Result.Failure($"Failed to save file: {ex.Message}");
+            }
         }
 
         /// <summary>
         /// Loads a document from the specified file path.
         /// </summary>
         /// <param name="filePath">The file path to load from</param>
-        /// <returns>The loaded document</returns>
+        /// <returns>Result containing the loaded document or error message</returns>
-        /// <exception cref="IOException">Thrown when file cannot be read</exception>
+        public Result<Document> Load(string filePath)
-        /// <exception cref="JsonException">Thrown when file contains invalid JSON</exception>
-        public Document Load(string filePath)
         {
-            var json = File.ReadAllText(filePath);
+            try
-            var document = JsonConvert.DeserializeObject<Document>(json);
+            {
-            return document;
+                var json = File.ReadAllText(filePath);
+                var document = JsonConvert.DeserializeObject<Document>(json);
+                return Result<Document>.Success(document);
+            }
+            catch (Exception ex)
+            {
+                return Result<Document>.Failure($"Failed to load file: {ex.Message}");
+            }
         }
 
         /// <summary>
         /// Validates that a document has the minimum required data.
         /// </summary>
         /// <param name="document">The document to validate</param>
-        /// <param name="validationMessage">Output parameter containing validation error message</param>
+        /// <returns>Result indicating success or failure with validation error message</returns>
-        /// <returns>True if document is valid, false otherwise</returns>
+        public Result Validate(Document document)
-        public bool Validate(Document document, out string validationMessage)
         {
             if (document.PartsToNest == null || document.PartsToNest.Count == 0)
             {
-                validationMessage = "No parts to nest.";
+                return Result.Failure("No parts to nest.");
-                return false;
             }
 
             if (document.StockBins == null || document.StockBins.Count == 0)
             {
-                validationMessage = "No stock bins available.";
+                return Result.Failure("No stock bins available.");
-                return false;
             }
 
-            validationMessage = string.Empty;
+            return Result.Success();
-            return true;
         }
     }
 }