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/FileDialog.xaml

@@ -4,11 +4,11 @@
      and Open/Save behavior. The property surface deliberately mirrors the Win32 dialogs
      (Title, Filter, FilterIndex, FileName, InitialDirectory, DefaultExt, ...) so a call site
      changes by one word. -->
-<Window x:Class="KillerPDF.Controls.FileDialog"
+<Window x:Class="MmdPdf.Controls.FileDialog"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        xmlns:kui="clr-namespace:KillerPDF.Controls"
-        Title="KillerPDF"
+        xmlns:kui="clr-namespace:MmdPdf.Controls"
+        Title="MMD PDF"
         Width="720" Height="520" MinWidth="560" MinHeight="420"
         WindowStyle="None" ResizeMode="CanResize" ShowInTaskbar="False"
         AllowsTransparency="True"