Perhaps it was inevitable — what goes up, up, up, must come down eventually. Homes in the Bay Area are now selling for less than they were a year ago, the only part of California where that is true, as rising interest rates continue to throw cold water on the region’s once-scorching pandemic real estate market. In September, the median price of existing single-family houses in the nine-county region was down 2.6% compared to the same month in 2021, albeit a still-pricey $1.26 million, according to data from the California Association of Realtors. That was the third consecutive month of year-ov…