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/KeyboardShortcuts.cs

@@ -16,10 +16,10 @@ 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
     {
@@ -147,7 +147,7 @@ namespace KillerPDF
             {
                 // A cancellable long operation (OCR, repair) is running behind the busy overlay - offer to
                 // cancel it instead of letting Escape fall through to the app-exit handler below.
-                if (KillerDialog.Show(this, string.Format(Loc("Str_Dlg_CancelBusy"), _busyOpLabel), "KillerPDF",
+                if (KillerDialog.Show(this, string.Format(Loc("Str_Dlg_CancelBusy"), _busyOpLabel), "MmdPdf",
                         MessageBoxButton.YesNo, MessageBoxImage.Question) == MessageBoxResult.Yes)
                     _busyCts?.Cancel();
                 e.Handled = true;
@@ -698,7 +698,7 @@ namespace KillerPDF
         // Opens the online help / how-to page in the user's default browser.
         private void OnlineHelp_Click(object sender, RoutedEventArgs e)
         {
-            try { Process.Start(new ProcessStartInfo("https://killerpdf.net/help.html") { UseShellExecute = true }); }
+            try { Process.Start(new ProcessStartInfo("https://baobab-ts.com/help.html") { UseShellExecute = true }); }
             catch { }
         }
     }