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/TransformWindow.cs

@@ -6,9 +6,9 @@ using System.Windows.Media;
 using System.Windows.Media.Imaging;
 using System.Windows.Shapes;
 using System.Windows.Threading;
-using KillerPDF.Services;
+using MmdPdf.Services;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     /// <summary>
     /// Modal "Transform" window. Renders the current page on its own canvas (so the main view's mode is
@@ -85,7 +85,7 @@ namespace KillerPDF
             _srcH = src.PixelHeight;
             _pageWpt = pageWpt;
             _pageHpt = pageHpt;
-            Title = "KillerPDF - " + S("Str_Tf_Suffix");
+            Title = "MmdPdf - " + S("Str_Tf_Suffix");
             Width = 980;
             Height = 720;
             MinWidth = 640;
@@ -367,7 +367,7 @@ namespace KillerPDF
             // Family shadow under the content pane, like the main window (flat on 98SE).
             root.Children.Add(UiKit.PaneWithShadow(previewWrap));
 
-            Content = DialogChrome.Frame(this, Owner, "KillerPDF - " + S("Str_Tf_Suffix"), () => { Applied = false; Close(); }, root);
+            Content = DialogChrome.Frame(this, Owner, "MmdPdf - " + S("Str_Tf_Suffix"), () => { Applied = false; Close(); }, root);
             UpdatePreview();   // populate the output-size readout at the original dimensions
 
             // Esc-to-close is wired by DialogChrome.Frame; Enter commits.