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/PdfiumInterop.cs

@@ -2,11 +2,11 @@ using System.IO;
 using System.Runtime.InteropServices;
 using Docnet.Core;
 
-namespace KillerPDF.Services
+namespace MmdPdf.Services
 {
     // ============================================================
     // Direct PDFium P/Invoke - the ONE home for every direct
-    // pdfium.dll call in the app (KillerUI refactor; formerly split
+    // pdfium.dll call in the app (MmdPdfUI refactor; formerly split
     // across FileOperations.cs and Links.cs).
     //
     // THREADING: PDFium is single-threaded. Docnet serializes every
@@ -410,7 +410,7 @@ namespace KillerPDF.Services
                 var doc = FPDF_LoadDocument(sourcePath, null);
                 if (doc == IntPtr.Zero)
                 {
-                    try { File.AppendAllText(System.IO.Path.Combine(System.IO.Path.GetTempPath(), "killerpdf_pdfium_debug.txt"), $"[{DateTime.Now:yyyy-MM-dd HH:mm:ss}] FPDF_LoadDocument returned null for: {sourcePath}\n\n"); } catch { }
+                    try { File.AppendAllText(System.IO.Path.Combine(System.IO.Path.GetTempPath(), "mmdpdf_pdfium_debug.txt"), $"[{DateTime.Now:yyyy-MM-dd HH:mm:ss}] FPDF_LoadDocument returned null for: {sourcePath}\n\n"); } catch { }
                     return false;
                 }
                 try
@@ -459,7 +459,7 @@ namespace KillerPDF.Services
                 try
                 {
                     File.AppendAllText(
-                        System.IO.Path.Combine(System.IO.Path.GetTempPath(), "killerpdf_pdfium_debug.txt"),
+                        System.IO.Path.Combine(System.IO.Path.GetTempPath(), "mmdpdf_pdfium_debug.txt"),
                         $"[{DateTime.Now:yyyy-MM-dd HH:mm:ss}] TryPdfiumSaveWithZeroRotations failed\n" +
                         $"  source: {sourcePath}\n" +
                         $"  type:   {ex.GetType().FullName}\n" +