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.

Controls/FileDialog.xaml.cs

@@ -11,7 +11,7 @@ using System.Windows.Controls;
 using System.Windows.Input;
 using System.Windows.Media.Imaging;
 
-namespace KillerPDF.Controls
+namespace MmdPdf.Controls
 {
     /// <summary>Open or Save. Picked at construction; changes the accept button and the rules.</summary>
     public enum FileDialogMode { Open, Save }
@@ -1261,14 +1261,14 @@ namespace KillerPDF.Controls
 
                 if (OverwritePrompt && File.Exists(full))
                 {
-                    // Killendar asks this through its own ConfirmDialog. KillerPDF already has a
+                    // Killendar asks this through its own ConfirmDialog. MmdPdf already has a
                     // themed confirm (KillerDialog) that every other prompt in the app uses, so
                     // this goes through that instead of importing a second one - two dialogs that
                     // ask the same kind of question is exactly how a UI starts to look stitched
                     // together. Same question, same buttons, one implementation.
                     var answer = KillerDialog.Show(this,
                         string.Format(Loc("Str_Dlg_OverwriteMsg"), Path.GetFileName(full)),
-                        "KillerPDF", MessageBoxButton.YesNo, MessageBoxImage.Warning);
+                        "MmdPdf", MessageBoxButton.YesNo, MessageBoxImage.Warning);
                     if (answer != MessageBoxResult.Yes) { FileNameBox.Focus(); return; }
                 }
             }