refactor: Extract duplicate code in MainForm and CutListTools

Consolidate duplicate logic to reduce code smells identified by Roslyn Bridge:
- Extract FlushPendingEdits() helper from Save() and Run() methods
- Simplify ClearData() to delegate to LoadDocumentData()
- Extract ConvertParts(), ConvertStockBins(), RunPackingAlgorithm() helpers
- Move DTO classes to separate Models.cs file

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

CutList.Mcp/Models.cs

@@ -0,0 +1,83 @@
+namespace CutList.Mcp;
+
+// Input models
+public class PartInput
+{
+    public string Name { get; set; } = string.Empty;
+    public string Length { get; set; } = string.Empty;
+    public int Quantity { get; set; } = 1;
+}
+
+public class StockBinInput
+{
+    public string Length { get; set; } = string.Empty;
+    public int Quantity { get; set; } = -1;  // -1 = unlimited
+    public int Priority { get; set; } = 25;   // Lower = used first
+}
+
+// Output models
+public class CutListResult
+{
+    public bool Success { get; set; }
+    public string? Error { get; set; }
+    public List<ResultBin> Bins { get; set; } = new();
+    public List<ResultItem> UnusedItems { get; set; } = new();
+    public CutListSummary? Summary { get; set; }
+}
+
+public class ResultBin
+{
+    public string Length { get; set; } = string.Empty;
+    public double LengthInches { get; set; }
+    public string UsedLength { get; set; } = string.Empty;
+    public double UsedLengthInches { get; set; }
+    public string RemainingLength { get; set; } = string.Empty;
+    public double RemainingLengthInches { get; set; }
+    public double Utilization { get; set; }
+    public List<ResultItem> Items { get; set; } = new();
+}
+
+public class ResultItem
+{
+    public string Name { get; set; } = string.Empty;
+    public string Length { get; set; } = string.Empty;
+    public double LengthInches { get; set; }
+}
+
+public class CutListSummary
+{
+    public int TotalBinsUsed { get; set; }
+    public int TotalPartsPlaced { get; set; }
+    public int TotalPartsNotPlaced { get; set; }
+    public string TotalStockLength { get; set; } = string.Empty;
+    public double TotalStockLengthInches { get; set; }
+    public string TotalWaste { get; set; } = string.Empty;
+    public double TotalWasteInches { get; set; }
+    public double OverallUtilization { get; set; }
+}
+
+public class ParseLengthResult
+{
+    public bool Success { get; set; }
+    public string? Error { get; set; }
+    public double Inches { get; set; }
+    public string? Formatted { get; set; }
+}
+
+public class FormatLengthResult
+{
+    public bool Success { get; set; }
+    public string? Error { get; set; }
+    public string? Formatted { get; set; }
+    public double Inches { get; set; }
+}
+
+public class CutListReportResult
+{
+    public bool Success { get; set; }
+    public string? Error { get; set; }
+    public string? FilePath { get; set; }
+    public int TotalBins { get; set; }
+    public int TotalParts { get; set; }
+    public int PartsNotPlaced { get; set; }
+}