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/BitmapHelpers.cs

@@ -4,11 +4,11 @@ using System.Windows;
 using System.Windows.Media;
 using System.Windows.Media.Imaging;
 
-namespace KillerPDF.Services
+namespace MmdPdf.Services
 {
     // ============================================================
     // Raw-bitmap helpers - pure functions over BGRA pixel buffers,
-    // no window state. Formerly a MainWindow partial (KillerUI
+    // no window state. Formerly a MainWindow partial (MmdPdfUI
     // refactor); shared by the render paths, thumbnails, page
     // export, OCR and the CLI.
     // ============================================================
@@ -180,7 +180,7 @@ namespace KillerPDF.Services
         /// <summary>
         /// Encodes raw BGRA pixel data to JPEG (quality 90) via WPF's encoder. Born as the CLI's
         /// CliEncodeJpeg (no JPEG encoder existed before --to-image); homed here beside RenderToPng
-        /// in the KillerUI refactor, shared by the CLI and the GUI image export.
+        /// in the MmdPdfUI refactor, shared by the CLI and the GUI image export.
         /// </summary>
         internal static byte[] EncodeJpeg(byte[] bgra, int width, int height, double dpi = 96)
         {