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/ShortcutTable.cs

@@ -1,6 +1,6 @@
 using System.Linq;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     // ============================================================
     // THE shortcut table. One source of truth for both views of the shortcuts overlay: the list
@@ -12,7 +12,7 @@ namespace KillerPDF
     // another while the code did neither consistently. Deriving both views from one array means a
     // binding cannot be described two ways, and ShortcutTableTests holds that.
     //
-    // Deliberately free of WPF and of MainWindow, so KillerPDF.Tests can link the file the way it
+    // Deliberately free of WPF and of MainWindow, so MmdPdf.Tests can link the file the way it
     // links OcrCatalog.cs. Anything that needs a Brush or a Control belongs in the overlay files.
     // ============================================================