dsh-mc-companion: Turn DeepSeek Harness (DSH) into a Minecraft buddy

`dsh-mc-companion` is an in-game social plugin for Minecraft within the DSH ecosystem, focusing on chat, following, memory, and interaction. It is not responsible for launching the game or downloading versions (handled by `dsh-mc-agent`). It must be used in conjunction with `dsh-mc-agent` and relies on the Cordis shared service. Core functions include automatically following players (within a 3-block distance), supporting in-game Chinese chat and specific commands (such as `/跟着我` and `/停下`), storing up to 60 local memories (located at `~/.dsh-mc/companion.json`, permissions 0600), switching moods based on context and probabilistically initiating conversation, as well as responding to events such as players joining and dying. Additionally, it injects status notifications into DSH and exposes `mc_friend`.