By Zaheer Kachwala and Joel Jose March 13 (Reuters) - Adobe's battered shares fell another 6% on Friday as news that the Photoshop maker's long-time CEO ‌would step down cast fresh doubts over its strategy to battle mounting ‌AI competition. Shantanu Narayen is credited with crafting the modern Adobe by turning its creative tools into ​a subscription service with more reliable revenue. But an influx of artificial intelligence rivals that can create images at low cost and with a simple text prompt has in ...