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.

Features/Viewer/IViewerHost.cs

@@ -1,9 +1,9 @@
 using System.Windows;
 using System.Windows.Input;
 using System.Windows.Controls;
-using KillerPDF.Controls;
+using MmdPdf.Controls;
 
-namespace KillerPDF.Features
+namespace MmdPdf.Features
 {
     /// <summary>
     /// What a document viewer needs from the window around it.

Features/Viewer/MainWindowTabStubs.cs

@@ -1,6 +1,6 @@
 using System.Collections.Generic;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     /// <summary>
     /// The tab and session members under the names the window already calls them by, routed to the

Features/Viewer/MainWindowViewerBridge.cs

@@ -6,7 +6,7 @@ using System.Windows.Media;
 using System.Windows.Shapes;
 using PdfSharpCore.Pdf;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     /// <summary>
     /// The window's half of the viewer bridge. Read this alongside

Features/Viewer/MainWindowViewerElements.cs

@@ -1,7 +1,7 @@
 using System.Windows.Controls;
-using KillerPDF.Controls;
+using MmdPdf.Controls;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     // The element names MainWindow.xaml used to generate, now that the document pane is a control
     // (Controls/PdfViewer.xaml).

Features/Viewer/MainWindowViewerHost.cs

@@ -1,11 +1,11 @@
-using KillerPDF.Features;
-using KillerPDF.Controls;
+using MmdPdf.Features;
+using MmdPdf.Controls;
 using System.Windows;
 using System.Windows.Input;
 using System;
 using System.Linq;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     // MainWindow's half of IViewerHost.
     //

Features/Viewer/MainWindowViewerStubs.cs

@@ -5,7 +5,7 @@ using System.Windows.Input;
 using System.Windows.Media;
 using PdfSharpCore.Pdf;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     /// <summary>
     /// Outward stubs: the annotation, text, crop, form and link members under the names the rest of