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/ProtocolRegistrar.cs

@@ -2,12 +2,12 @@ using System;
 using System.Diagnostics;
 using Microsoft.Win32;
 
-namespace KillerPDF.Services
+namespace MmdPdf.Services
 {
     internal static class ProtocolRegistrar
     {
-        internal const string Scheme = "killerpdf";
-        private const string RegistryPath = @"Software\Classes\killerpdf";
+        internal const string Scheme = "mmdpdf";
+        private const string RegistryPath = @"Software\Classes\mmdpdf";
 
         internal static void Register() => Register(Registry.CurrentUser, null);
 
@@ -22,14 +22,14 @@ namespace KillerPDF.Services
                 appPath ??= Process.GetCurrentProcess().MainModule!.FileName;
                 using var protocol = root.CreateSubKey(RegistryPath);
                 if (protocol == null) return;
-                protocol.SetValue("", "URL:KillerPDF Protocol");
+                protocol.SetValue("", "URL:MmdPdf Protocol");
                 protocol.SetValue("URL Protocol", "");
                 using (var icon = protocol.CreateSubKey("DefaultIcon"))
                     icon?.SetValue("", $"\"{appPath}\",0");
                 using (var command = protocol.CreateSubKey(@"shell\open\command"))
                     command?.SetValue("", $"\"{appPath}\" \"%1\"");
             }
-            catch (Exception ex) { Debug.WriteLine($"Failed to register KillerPDF protocol: {ex.Message}"); }
+            catch (Exception ex) { Debug.WriteLine($"Failed to register MmdPdf protocol: {ex.Message}"); }
         }
 
         internal static void Unregister() => Unregister(Registry.CurrentUser);