Fix TTM_ADDTOOL : manifeste Windows Common Controls 6.0

- app.manifest : active comctl32 v6 (requis par walk) + DPI awareness
- rsrc.syso : manifeste + icone exe embarques dans le binaire via rsrc
- build.bat : genere rsrc.syso automatiquement avant go build

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

build.bat

@@ -19,6 +19,14 @@ if errorlevel 1 (
     exit /b 1
 )
 
+echo [*] Generation du manifeste Windows (rsrc.syso)...
+where rsrc >nul 2>&1
+if errorlevel 1 (
+    echo [*] Installation de rsrc...
+    go install github.com/akavel/rsrc@latest
+)
+rsrc -manifest app.manifest -ico icon.ico -o rsrc.syso
+
 echo [*] Compilation en cours...
 go build -ldflags "-H windowsgui -s -w" -o GitUpdateChecker.exe .