feat: rebrand to MMD PDF, single corporate theme, and remove original text under an edit

- Services/PdfRedactText.cs: strip text whose origin falls inside a CoverAnnotation
  from the page content stream at save time, hooked into PdfBurn.DrawAnnotationsIntoDoc.
  Fixes edited values staying recoverable by text extraction.
- Themes/MMD.xaml replaces all thirteen themes; picker and accent strip removed; no dark mode.
- Rename KillerPDF -> MMD PDF across code, resources, packaging and locale strings; new icon.
- Remove the upstream author credit and the in-app install button.

Shell/DragDrop.cs

@@ -17,10 +17,10 @@ using Microsoft.Win32;
 using PdfSharpCore.Drawing;
 using PdfSharpCore.Pdf;
 using PdfSharpCore.Pdf.IO;
-using KillerPDF.Services;
+using MmdPdf.Services;
 using PdfPigDoc = UglyToad.PdfPig.PdfDocument;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     public partial class MainWindow
     {
@@ -154,7 +154,7 @@ namespace KillerPDF
         {
             var ask = KillerDialog.Show(this,
                 string.Format(Loc("Str_Dlg_RepairAsk"), System.IO.Path.GetFileName(path)),
-                "KillerPDF", MessageBoxButton.YesNo, MessageBoxImage.Warning);
+                "MmdPdf", MessageBoxButton.YesNo, MessageBoxImage.Warning);
             if (ask != MessageBoxResult.Yes) return null;
 
             var busy = ShowBusyOverlay(Loc("Str_Busy_Repairing"));
@@ -174,7 +174,7 @@ namespace KillerPDF
                 if (repaired is null)
                     KillerDialog.Show(this,
                         $"\"{System.IO.Path.GetFileName(path)}\" could not be repaired.",
-                        "KillerPDF", MessageBoxButton.OK, MessageBoxImage.Error);
+                        "MmdPdf", MessageBoxButton.OK, MessageBoxImage.Error);
                 return repaired;
             }
             finally { HideBusyOverlay(busy); }