chore: 合并 Maildir 修复与 README 更新

apps/api/internal/app/maildir_ownership_unix.go

@@ -0,0 +1,17 @@
+//go:build unix
+
+package app
+
+import "os"
+
+const (
+	maildirOwnerUID = 5000
+	maildirOwnerGID = 5000
+)
+
+func applyMaildirOwnership(path string) error {
+	if os.Geteuid() != 0 {
+		return nil
+	}
+	return os.Chown(path, maildirOwnerUID, maildirOwnerGID)
+}