fix(models): correct DeepSeek V4 Flash cache rate, add xiaomi models

DeepSeek V4 Flash cache-read rate was /bin/bash.01/1M but docs list ~/bin/bash.028.
Added xiaomi/mimo-v2.5-pro and xiaomi/mimo-v2.5 to MODEL_COSTS so they
don't display as zero-cost models (pricing TBD, currently set to 0).