feat(shapes): add PlateSizes catalog and wire Ctrl+P to snap-to-standard

PlateSizes holds standard mill sheet sizes (48x96 through 96x240) and
exposes Recommend() which snaps small layouts to an increment and
rounds larger layouts up to the nearest fitting sheet. Plate.SnapToStandardSize
applies the result while preserving long-axis orientation, and the
existing Ctrl+P "Resize to Fit" menu in EditNestForm now calls it
instead of the simple round-up AutoSize.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Core/Plate.cs

@@ -1,6 +1,7 @@
 using OpenNest.Collections;
 using OpenNest.Geometry;
 using OpenNest.Math;
+using OpenNest.Shapes;
 using System;
 using System.Collections.Generic;
 using System.Linq;
@@ -548,6 +549,65 @@ namespace OpenNest
                 Rounding.RoundUpToNearest(xExtent, roundingFactor));
         }
 
+        /// <summary>
+        /// Sizes the plate using the <see cref="PlateSizes"/> catalog: small
+        /// layouts snap to an increment, larger ones round up to the next
+        /// standard mill sheet. The plate's long-axis orientation (X vs Y)
+        /// is preserved. Does nothing if the plate has no parts.
+        /// </summary>
+        public PlateSizeResult SnapToStandardSize(PlateSizeOptions options = null)
+        {
+            if (Parts.Count == 0)
+                return default;
+
+            var bounds = Parts.GetBoundingBox();
+
+            // Quadrant-aware extents relative to the plate origin, matching AutoSize.
+            double xExtent;
+            double yExtent;
+
+            switch (Quadrant)
+            {
+                case 1:
+                    xExtent = System.Math.Abs(bounds.Right) + EdgeSpacing.Right;
+                    yExtent = System.Math.Abs(bounds.Top) + EdgeSpacing.Top;
+                    break;
+
+                case 2:
+                    xExtent = System.Math.Abs(bounds.Left) + EdgeSpacing.Left;
+                    yExtent = System.Math.Abs(bounds.Top) + EdgeSpacing.Top;
+                    break;
+
+                case 3:
+                    xExtent = System.Math.Abs(bounds.Left) + EdgeSpacing.Left;
+                    yExtent = System.Math.Abs(bounds.Bottom) + EdgeSpacing.Bottom;
+                    break;
+
+                case 4:
+                    xExtent = System.Math.Abs(bounds.Right) + EdgeSpacing.Right;
+                    yExtent = System.Math.Abs(bounds.Bottom) + EdgeSpacing.Bottom;
+                    break;
+
+                default:
+                    return default;
+            }
+
+            // PlateSizes.Recommend takes (short, long); canonicalize then map
+            // the result back so the plate's long axis stays aligned with the
+            // parts' long axis.
+            var shortDim = System.Math.Min(xExtent, yExtent);
+            var longDim = System.Math.Max(xExtent, yExtent);
+            var result = PlateSizes.Recommend(shortDim, longDim, options);
+
+            // Plate convention: Length = X axis, Width = Y axis.
+            if (xExtent >= yExtent)
+                Size = new Size(result.Width, result.Length);   // X is the long axis
+            else
+                Size = new Size(result.Length, result.Width);   // Y is the long axis
+
+            return result;
+        }
+
         /// <summary>
         /// Gets the area of the top surface of the plate.
         /// </summary>