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.

validation/QpdfSweep.ps1

@@ -5,7 +5,7 @@
 
 .DESCRIPTION
     The second half of the release validation (Compare-VeraPDF.ps1 is the first). Reads the
-    resave log written by `KillerPDF.exe --batch-resave` and checks only the rows marked OK -
+    resave log written by `MmdPdf.exe --batch-resave` and checks only the rows marked OK -
     skipped files were never written and have nothing to compare.
 
     qpdf exit codes: 0 = clean, 2 = errors, 3 = warnings only. "Worsened" is any pair whose
@@ -18,7 +18,7 @@
 
 .NOTES
     Compatible with Windows PowerShell 5.1 and PowerShell 7.
-    Part of the KillerPDF validation harness (validation/).
+    Part of the MmdPdf validation harness (validation/).
 #>
 [CmdletBinding()]
 param(