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>

logger.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+var logFile *os.File
+
+func initLogger() {
+	dir := filepath.Join(exeDir(), "log")
+	os.MkdirAll(dir, 0755)
+
+	// Nettoyage logs > 30 jours
+	entries, _ := os.ReadDir(dir)
+	cutoff := time.Now().AddDate(0, 0, -30)
+	for _, e := range entries {
+		if !e.IsDir() {
+			if info, err := e.Info(); err == nil && info.ModTime().Before(cutoff) {
+				os.Remove(filepath.Join(dir, e.Name()))
+			}
+		}
+	}
+
+	logPath := filepath.Join(dir, time.Now().Format("2006-01-02")+".log")
+	f, err := os.OpenFile(logPath, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
+	if err != nil {
+		return
+	}
+	logFile = f
+}
+
+func logMsg(level, msg string) {
+	line := fmt.Sprintf("[%s] %-5s %s\n", time.Now().Format("15:04:05"), level, msg)
+	if logFile != nil {
+		logFile.WriteString(line)
+	}
+}
+
+func logInfo(msg string)  { logMsg("INFO", msg) }
+func logWarn(msg string)  { logMsg("WARN", msg) }
+func logError(msg string) { logMsg("ERROR", msg) }