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/Viewer/PdfViewer.Tabs.cs

@@ -6,9 +6,9 @@ using System.Windows;
 using System.Windows.Controls;
 using PdfSharpCore.Pdf;
 
-namespace KillerPDF.Controls
+namespace MmdPdf.Controls
 {
-    // Tabbed document support. KillerPDF keeps one window and one live "working set" of
+    // Tabbed document support. MmdPdf keeps one window and one live "working set" of
     // per-document fields (in MainWindow.xaml.cs). Each open PDF is a DocumentSession that
     // owns its own copy of those fields. Switching tabs captures the live fields into the
     // outgoing session and applies the incoming session's fields, then re-renders.
@@ -790,7 +790,7 @@ namespace KillerPDF.Controls
             {
                 var res = KillerDialog.Show(Host!.Window,
                     Loc("Str_Dlg_UnsavedClose"),
-                    "KillerPDF", MessageBoxButton.YesNo, MessageBoxImage.Warning);
+                    "MmdPdf", MessageBoxButton.YesNo, MessageBoxImage.Warning);
                 if (res != MessageBoxResult.Yes) { RebuildTabStrip(); return; }
             }
 
@@ -838,7 +838,7 @@ namespace KillerPDF.Controls
             if (docTabs.Any(t => t.IsDirty))
             {
                 var res = KillerDialog.Show(Host!.Window, Loc("Str_Dlg_UnsavedCloseAll"),
-                    "KillerPDF", MessageBoxButton.YesNo, MessageBoxImage.Warning);
+                    "MmdPdf", MessageBoxButton.YesNo, MessageBoxImage.Warning);
                 if (res != MessageBoxResult.Yes) { RebuildTabStrip(); return; }
             }