By Tom Balmforth MOSCOW (Reuters) – An activist ally of Kremlin critic Alexei Navalny told Reuters on Thursday she had fled Russia to avoid arrest, while two of his top aides said they had received letters with threats to themselves and their families. Violetta Grudina, who was barred from standing for election last year in the Arctic port city of Murmansk, did not say where she had gone, when she had left or how. “There wasn’t much choice. I’m on a wanted list in Russia and prison lies in store for me,” Grudina said in a short message sent via the Telegram app. She joined numerous opposition …