deepseek-coder and deepseek-chat merge into DeepSeek V2.5

deepseek-coder & deepseek-chat 升级为 DeepSeek V2.5 模型

DeepSeek V2 Chat and DeepSeek Coder V2 have been merged and upgraded into DeepSeek V2.5. API users reach the new model through either deepseek-coder or deepseek-chat.

Why it matters: DeepSeek merged its chat and code models into V2.5 while keeping both existing API names so current call patterns still work.