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/KeyboardMapOverlay.cs

@@ -5,7 +5,7 @@ using System.Windows.Media;
 using System.Windows.Media.Animation;
 using System.Windows.Shapes;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     // ============================================================
     // Visual keyboard for the shortcuts overlay.
@@ -19,7 +19,7 @@ namespace KillerPDF
     public partial class MainWindow
     {
         // KbLayer, the binding table and its types live in Services/ShortcutTable.cs, which is free
-        // of WPF so KillerPDF.Tests can link it.
+        // of WPF so MmdPdf.Tests can link it.
         private KbLayer _kbLayer = KbLayer.Base;
         private bool _kbBuilt;
         private TextBlock? _kbDetail;
@@ -187,7 +187,7 @@ namespace KillerPDF
                     key.SetResourceReference(Border.CornerRadiusProperty, "ControlCornerRadius");
                     key.SetResourceReference(Border.BackgroundProperty, "KeyboardKeyBrush");
                     key.SetResourceReference(Border.BorderBrushProperty, "CardBorderBrush");
-                    // Hover: the keycap lifts a few pixels, like the cards on the killertools.net front page.
+                    // Hover: the keycap lifts a few pixels, like the cards on the baobab-ts.com front page.
                     var lift = new TranslateTransform();
                     key.RenderTransform = lift;
                     string keyId = id;