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.

MmdPdf.Tests/PdfFontStyleTests.cs

@@ -0,0 +1,28 @@
+using MmdPdf.Services;
+using Xunit;
+
+namespace MmdPdf.Tests
+{
+    public class PdfFontStyleTests
+    {
+        [Theory]
+        // #187: families are normalized to the installed Windows family the PostScript name
+        // means - the raw PS name resolves to nothing in WPF and read as "all formatting lost".
+        [InlineData("ABCDEF+Helvetica-Bold", "Arial", true, false)]
+        [InlineData("Helvetica-Oblique", "Arial", false, true)]
+        [InlineData("TimesNewRomanPS-BoldItalicMT", "Times New Roman", true, true)]
+        [InlineData("Arial-Regular", "Arial", false, false)]
+        [InlineData("ArialMT", "Arial", false, false)]
+        [InlineData("TimesNewRomanPSMT", "Times New Roman", false, false)]
+        [InlineData("CourierNewPS-BoldMT", "Courier New", true, false)]
+        [InlineData("GHIJKL+BookAntiqua", "Book Antiqua", false, false)]
+        public void DetectsFaceStyleFromPdfFontName(string source, string family, bool bold, bool italic)
+        {
+            var detected = PdfFontStyle.FromPdfName(source);
+
+            Assert.Equal(family, detected.Family);
+            Assert.Equal(bold, detected.Bold);
+            Assert.Equal(italic, detected.Italic);
+        }
+    }
+}