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.

Models/EditingTypes.cs

@@ -2,7 +2,7 @@ using System;
 using System.Windows;
 using System.Windows.Media;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     public enum EditTool { Select, Text, Highlight, Strikethrough, Underline, Draw, Signature, Image, Crop, Line, Rotate, Shape }
 

Models/LinkTypes.cs

@@ -1,4 +1,4 @@
-namespace KillerPDF
+namespace MmdPdf
 {
     /// <summary>
     /// One link rectangle on a page, in render-dim coordinates.

Models/PageThumbnailVm.cs

@@ -8,7 +8,7 @@ using System.Windows.Media.Imaging;
 using Docnet.Core;
 using Docnet.Core.Models;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     /// <summary>
     /// ViewModel for a single page thumbnail in the sidebar PageList.
@@ -88,7 +88,7 @@ namespace KillerPDF
                 using var pr = docReader.GetPageReader(pageIndex);
                 int tw  = pr.GetPageWidth();
                 int th  = pr.GetPageHeight();
-                var raw = KillerPDF.Services.PdfiumInterop.RenderPageWithAnnotations(filePath, pageIndex, tw, th)
+                var raw = MmdPdf.Services.PdfiumInterop.RenderPageWithAnnotations(filePath, pageIndex, tw, th)
                     ?? pr.GetImage();   // #141
                 if (tw <= 0 || th <= 0 || raw == null || raw.Length < tw * th * 4)
                     return null;

Models/StampModels.cs

@@ -1,6 +1,6 @@
 using System.Windows.Media;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     internal enum StampKind { PageNumber, Watermark }
 

Models/UndoTypes.cs

@@ -1,14 +1,14 @@
 using System.Collections.Generic;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     // The undo stack's entry type. Each entry is either an annotation removal or a full document
     // snapshot; AnnotationGroup removes a specific set in one step (a text edit = cover + text).
     //
     // TOP-LEVEL, not nested in MainWindow. The code that pushes undo entries - Annotations.cs and
-    // TextEditing.cs - lives in KillerPDF.Controls, where a type nested in MainWindow only spells
+    // TextEditing.cs - lives in MmdPdf.Controls, where a type nested in MainWindow only spells
     // as MainWindow.UndoEntry; that would mean qualifying roughly 30 call sites for no gain. As
-    // top-level types in KillerPDF they resolve unqualified from the child namespace too.
+    // top-level types in MmdPdf they resolve unqualified from the child namespace too.
     //
     // This also retires the CS0052 chain that made them internal in the first place: DocumentSession
     // had to be internal for the render cache, its UndoStack field is Stack<UndoEntry>, and a field

Models/ViewTypes.cs

@@ -1,11 +1,11 @@
-namespace KillerPDF
+namespace MmdPdf
 {
     // How a document view lays its pages out, and how it fits them to the viewport.
     //
-    // TOP-LEVEL, not nested in MainWindow. The viewer is a UserControl in KillerPDF.Controls, and
+    // TOP-LEVEL, not nested in MainWindow. The viewer is a UserControl in MmdPdf.Controls, and
     // from there a type nested in MainWindow only spells as MainWindow.ViewMode - which would mean
-    // qualifying 91 references for no gain. As top-level types in KillerPDF they resolve
-    // unqualified from KillerPDF.Controls too (a namespace declaration puts its parent namespaces
+    // qualifying 91 references for no gain. As top-level types in MmdPdf they resolve
+    // unqualified from MmdPdf.Controls too (a namespace declaration puts its parent namespaces
     // in scope), so every call site compiles untouched.
     //
     // internal, not public: nothing outside the assembly has any business with either.

Models/ViewerState.cs

@@ -1,7 +1,7 @@
 using System.Collections.Generic;
 using System.Windows.Controls;
 
-namespace KillerPDF
+namespace MmdPdf
 {
     /// <summary>
     /// Everything ONE document view owns. Split pane needs two of these; each PdfViewer control
@@ -15,7 +15,7 @@ namespace KillerPDF
     /// and zoom; it does NOT need a second copy of the per-document machinery, because each
     /// pane will simply own its own set of sessions.
     ///
-    /// TOP-LEVEL, not nested in MainWindow. The viewer lives in KillerPDF.Controls and cannot own a
+    /// TOP-LEVEL, not nested in MainWindow. The viewer lives in MmdPdf.Controls and cannot own a
     /// type nested in the window without every reference spelling out MainWindow.ViewerState.
     /// ViewMode and FitMode live in Models/ViewTypes.cs for the same reason.
     /// </summary>