Docs: remove old design logs, update for chat apps and MindGo

[rick-mingyu-liu]

Stacked on #36. Merge in order: #34, #35, #36, then this one.

Removed

• docs/design/humanlike-replies.md: a tuning log from 2026-09-24. Its results live in the prompts, and its attributions are in upstream-provenance.md.
• docs/design/wechat-transport.md: the notes still true about WeChat 4.x (sender matching, window capture for photos, the lock and runaway pause, voice mode) move into how-it-works.md. Everything else was history (iLink, sticker probes, typing status).

Updated

• README:
  • status: 319 tests, live health, Telegram and Opus;
  • new rows for the WeChat/iMessage agent and MindGo;
  • roadmap and the documentation table.
• Agent guide:
  • status as of 2026-09-27;
  • setup step 8 (chat apps);
  • the wechat, imessage and help commands;
  • WeChat and iMessage live checklists;
  • code layout (src/main.ts, messaging.ts, channels/, mindgo.ts).
• Architecture:
  • chat apps in the diagram, parts table and privacy table;
  • MindGo marked done;
  • the agent-cli.ts size.
• how-it-works.md: retitled "How the companion works", with the WeChat 4.x notes and a pointer to the agent in WeChat.
• README.zh-CN: the agent in Mandarin (wechat, imessage -m) and yes/no approvals.
• Links to the removed notes are fixed in the operations guides and provenance.

There are no code changes; 319 tests still pass.

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