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.

Shell/SystemMenu.cs

@@ -6,7 +6,7 @@ using System.Windows.Interop;
 using System.Windows.Media.Animation;
 
 // ============================================================
-// THEMED WINDOWS SYSTEM MENU (from KillerUI/Shell/SystemMenu.cs)
+// THEMED WINDOWS SYSTEM MENU (from MmdPdfUI/Shell/SystemMenu.cs)
 //
 // WindowChrome turns the title bar into a real native caption, which is what buys free snap,
 // drag and double-click-maximize - but it also means Windows answers a caption right-click
@@ -19,11 +19,11 @@ using System.Windows.Media.Animation;
 // WM_SYSCOMMAND the native menu would have sent, so behavior is identical - including Move and
 // Size, which hand off to Windows' own modal drag loops.
 //
-// KillerPDF adaptations: HTCAPTION already lives in Shell/WindowChrome.cs (not redeclared
+// MmdPdf adaptations: HTCAPTION already lives in Shell/WindowChrome.cs (not redeclared
 // here), the menu comes from MakeThemedMenu() so its TextOptions match the app's other
-// code-built menus, and the kit's Anim.FadeIn is inlined (KillerPDF carries no Anim class).
+// code-built menus, and the kit's Anim.FadeIn is inlined (MmdPdf carries no Anim class).
 // ============================================================
-namespace KillerPDF
+namespace MmdPdf
 {
     public partial class MainWindow
     {
@@ -90,7 +90,7 @@ namespace KillerPDF
                 };
             }
 
-            // KillerPDF keeps its implicit ContextMenu/MenuItem styles in MainWindow.xaml's
+            // MmdPdf keeps its implicit ContextMenu/MenuItem styles in MainWindow.xaml's
             // WINDOW resources (not App.xaml), and an Absolute-placement menu has no inheritance
             // context to find them through - it rendered stock white. PlacementTarget supplies
             // that context; with PlacementMode.Absolute it does not affect position.