feature/go-rewrite : base Go avec walk GUI

- Rewrite complet en Go : exe unique sans _internal/, sans extraction temp
- GUI Windows-native via github.com/lxn/walk (TableView, TextEdit, PushButton)
- Meme fonctionnalites : check repos, pull, checkout, auto-update, logs
- build.bat : go build -ldflags "-H windowsgui -s -w" -> 9.6 Mo, zero dependance

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

main.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+
+	"github.com/lxn/walk"
+)
+
+const VERSION = "0.7.0"
+
+func exeDir() string {
+	exe, err := os.Executable()
+	if err != nil {
+		return "."
+	}
+	return filepath.Dir(exe)
+}
+
+func fileExists(p string) bool {
+	_, err := os.Stat(p)
+	return err == nil
+}
+
+func main() {
+	runtime.LockOSThread()
+	initLogger()
+	logInfo(fmt.Sprintf("=== Demarrage Git Update Checker v%s ===", VERSION))
+
+	if err := runApp(); err != nil {
+		walk.MsgBox(nil, "Erreur fatale", err.Error(), walk.MsgBoxIconError)
+		os.Exit(1)
+	}
+}