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/ColorPickerDialog.cs

@@ -9,7 +9,7 @@ using System.Windows.Data;
 using System.Windows.Input;
 using System.Windows.Media;
 using System.Windows.Shapes;
-namespace KillerPDF
+namespace MmdPdf
 {
     /// <summary>
     /// A small, themed RGB color picker: saturation/value square + hue strip, RGB and HTML-hex inputs,
@@ -50,7 +50,7 @@ namespace KillerPDF
         private static string L(string key) => Application.Current.TryFindResource(key) as string ?? key;
         public ColorPickerDialog(Window? owner, Color initial)
         {
-            Title = "KillerPDF - " + L("Str_Color_Name");
+            Title = "MmdPdf - " + L("Str_Color_Name");
             Width = 300;
             SizeToContent = SizeToContent.Height;
             DialogChrome.Configure(this, owner);
@@ -359,7 +359,7 @@ namespace KillerPDF
             box.Padding = new Thickness(4, 0, 4, 0);
             return box;
         }
-        // A crosshair/target glyph drawn in vectors, to match the KillerPDF look.
+        // A crosshair/target glyph drawn in vectors, to match the MmdPdf look.
         private UIElement CrosshairIcon()
         {
             var g = new Grid { Width = 14, Height = 14 };