KABUL — An Afghan government commission blamed regulators for financial mismanagement at the nation’s largest private bank, saying Sunday that monitors should have kept Kabul Bank from making hundreds of millions of dollars in questionable loans that forced the bank into receivership. The bank has been in turmoil since the fall, when it was discovered that shareholders — some of them relatives or backers of President Hamid Karzai — had lent themselves millions to invest in mansions in Dubai, United Arab Emirates, and risky prestige projects such as an airline and shopping malls in Kabul.