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/LocaleManager.cs

@@ -2,7 +2,7 @@ using System;
 using System.IO;
 using System.Windows;
 
-namespace KillerPDF.Services
+namespace MmdPdf.Services
 {
     internal enum Locale { EnUS, Es, ZhTW, ZhCN, Bn, TrTR, De, Fr, JaJP, CsCZ, PlPL, HuHU }
 
@@ -66,8 +66,8 @@ namespace KillerPDF.Services
             {
                 if (TryApplyExternal()) { EnsureWatcher(); return; }
                 if (!_externalLoadedOnce)
-                    MessageBox.Show($"Could not load the translation file:\n{ExternalFile}\n\nCheck the path and the file's XML, then start KillerPDF again.",
-                                    "KillerPDF --lang-file", MessageBoxButton.OK, MessageBoxImage.Warning);
+                    MessageBox.Show($"Could not load the translation file:\n{ExternalFile}\n\nCheck the path and the file's XML, then start MmdPdf again.",
+                                    "MmdPdf --lang-file", MessageBoxButton.OK, MessageBoxImage.Warning);
                 // Fall through to the normal locale so the app still comes up usable.
             }