feat(posts): CI Fiber one program per sheet, configurable pallet change

Multi-sheet nests previously went into one program with a single header
size and one M50 at the end, so sheet 2 would cut into sheet 1's
skeleton. New Sheets settings:

- One program per sheet (default on): JOB.cnc -> JOB-1.cnc, JOB-2.cnc,
  each a full program with its own size and pallet change (CL-series
  batch rule, EM-423 7.4). Single-sheet nests keep the chosen name.
- Off: one program, with /L "L0" + pallet change between sheets;
  mixed sheet sizes are rejected.
- Pallet change code (default M50, unconfirmed for multi-sheet CI Fiber
  runs; documented as a release blocker).

All sheets are validated and rendered before any file is written.
IMultiFilePostProcessor lets the desktop app confirm overwrites of every
target file and list what was saved, and the console print each file.

Posts/OpenNest.Posts.CincinnatiCIFiber/CIFiberPostConfig.cs

@@ -16,23 +16,29 @@ namespace OpenNest.Posts.CincinnatiCIFiber
         Description = "Which CI Fiber table this configuration drives and the largest sheet it accepts."
     )]
     [PostSettingsSection(
-        MaterialSection,
+        SheetsSection,
         1,
+        Description = "How a nest with more than one sheet is written, and the code that swaps pallets."
+    )]
+    [PostSettingsSection(
+        MaterialSection,
+        2,
         Description = "Maps OpenNest material names to the controller's V.E.MATERIAL code."
     )]
     [PostSettingsSection(
         OutputSection,
-        2,
+        3,
         Description = "Number format, units, and what the posted program includes."
     )]
     [PostSettingsSection(
         MacrosSection,
-        3,
+        4,
         Description = "Controller subroutines called around each contour and at program start and end. They must exist on the machine."
     )]
     public class CIFiberPostConfig
     {
         private const string MachineSection = "Machine";
+        private const string SheetsSection = "Sheets";
         private const string MaterialSection = "Material";
         private const string OutputSection = "Program output";
         private const string MacrosSection = "Macros";
@@ -91,6 +97,35 @@ namespace OpenNest.Posts.CincinnatiCIFiber
         [PostSetting(MachineSection, 2, Minimum = 0, Maximum = 10000, DecimalPlaces = 3)]
         public double MaxTableY { get; set; } = 81.25;
 
+        /// <summary>
+        /// Write each sheet as its own program (NAME-1.cnc, NAME-2.cnc, ...), the
+        /// Cincinnati convention for batch runs. When false, every sheet goes into
+        /// one program with a pallet change between sheets. A nest with a single
+        /// sheet always posts to the chosen file name.
+        /// </summary>
+        [DisplayName("One program per sheet")]
+        [Description(
+            "Save each sheet as its own program: JOB.cnc becomes JOB-1.cnc, JOB-2.cnc, ... "
+                + "Clear to put every sheet in one program, with a pallet change between sheets. "
+                + "A single-sheet nest always saves to the chosen name."
+        )]
+        [PostSetting(SheetsSection, 0)]
+        public bool OneProgramPerSheet { get; set; } = true;
+
+        /// <summary>
+        /// Line written to swap pallets: after the last sheet, and between sheets
+        /// in a single program. M50 comes from the machine sample and the CL-series
+        /// manual (EM-423 §3.50); it is unconfirmed for multi-sheet CI Fiber runs.
+        /// Blank writes no pallet change.
+        /// </summary>
+        [DisplayName("Pallet change code")]
+        [Description(
+            "Written after each sheet to swap pallets. M50 matches the machine sample; "
+                + "confirm it for multi-sheet runs. Blank writes no pallet change."
+        )]
+        [PostSetting(SheetsSection, 1)]
+        public string PalletChangeCode { get; set; } = "M50";
+
         /// <summary>Skippable global subroutine used to cancel comp / park between features.</summary>
         [DisplayName("Layer: cancel (L0)")]
         [Description("Called before each contour and at the end to cancel compensation and park.")]