fix: resolve bugs found in pre-release review

internal/config/migrate.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"io"
 	"os"
 	"path/filepath"
 )
@@ -11,15 +12,54 @@ func MigrateLegacy(outputDir string) {
 		return
 	}
 
-	oldDB := filepath.Join(homeDir, ".godeez", "tracks.db")
+	oldDir := filepath.Join(homeDir, ".godeez")
+	oldDB := filepath.Join(oldDir, "tracks.db")
 	newDB := filepath.Join(outputDir, ".tracks.db")
 	if _, err := os.Stat(oldDB); err == nil {
 		if _, err := os.Stat(newDB); os.IsNotExist(err) {
-			os.Rename(oldDB, newDB)
+			if err := os.Rename(oldDB, newDB); err != nil {
+				if err := copyFile(oldDB, newDB); err != nil {
+					return
+				}
+				os.Remove(oldDB)
+			}
 		}
 	}
 
-	oldDir := filepath.Join(homeDir, ".godeez")
-	os.Remove(filepath.Join(oldDir, "config.toml"))
 	os.Remove(oldDir)
 }
+
+func copyFile(src, dst string) error {
+	in, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer in.Close()
+
+	out, err := os.CreateTemp(filepath.Dir(dst), ".tracks.db-*.tmp")
+	if err != nil {
+		return err
+	}
+	tmp := out.Name()
+
+	if _, err := io.Copy(out, in); err != nil {
+		out.Close()
+		os.Remove(tmp)
+		return err
+	}
+	if err := out.Sync(); err != nil {
+		out.Close()
+		os.Remove(tmp)
+		return err
+	}
+	if err := out.Close(); err != nil {
+		os.Remove(tmp)
+		return err
+	}
+	if err := os.Rename(tmp, dst); err != nil {
+		os.Remove(tmp)
+		return err
+	}
+
+	return nil
+}