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.

Services/ShellIcons.cs

@@ -4,11 +4,11 @@ using System.Windows.Interop;
 using System.Windows.Media;
 using System.Windows.Media.Imaging;
 
-namespace KillerPDF.Services
+namespace MmdPdf.Services
 {
     // ============================================================
     // File-type (shell) icons - split out of FileOperations.cs
-    // (KillerUI refactor). Same name as the KillerUI kit's
+    // (MmdPdfUI refactor). Same name as the MmdPdfUI kit's
     // Services/ShellIcons.cs, which the family file picker uses, so
     // the picker rollout lands on a familiar shape.
     //