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.

choco/tools/chocolateyUninstall.ps1

@@ -1,7 +1,7 @@
 $ErrorActionPreference = 'Stop'
 
-$installDir = Join-Path $env:ProgramFiles 'KillerPDF'
+$installDir = Join-Path $env:ProgramFiles 'MmdPdf'
 if (Test-Path $installDir) { Remove-Item $installDir -Recurse -Force }
 
-$startMenuPath = Join-Path $env:ProgramData 'Microsoft\Windows\Start Menu\Programs\KillerPDF.lnk'
+$startMenuPath = Join-Path $env:ProgramData 'Microsoft\Windows\Start Menu\Programs\MmdPdf.lnk'
 if (Test-Path $startMenuPath) { Remove-Item $startMenuPath -Force }