refactor: 프로젝트명 DB720Flasher → FirmwareFlasher

폴더·csproj·어셈블리명·RootNamespace·코드 namespace·x:Class·app.manifest 전부 변경.
빌드 결과가 네이티브로 FirmwareFlasher.exe 로 나온다(dist 수동 리네임 불필요).
README 빌드/구조 경로도 갱신. 모델명 "DB720"은 그대로 유지.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

FirmwareFlasher/App.xaml

@@ -0,0 +1,12 @@
+<Application x:Class="FirmwareFlasher.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             StartupUri="MainWindow.xaml">
+  <Application.Resources>
+    <ResourceDictionary>
+      <ResourceDictionary.MergedDictionaries>
+        <ResourceDictionary Source="Themes/Controls.xaml" />
+      </ResourceDictionary.MergedDictionaries>
+    </ResourceDictionary>
+  </Application.Resources>
+</Application>