Add Chinese translations of all three documents

Full translations rather than summaries, section-for-section with the English:
README (13 sections), AGENTS.md (21), and docs/reverse-proxy.md. Each pair
cross-links to the other and says the two are kept in step, since documentation
that has silently diverged is worse than documentation that does not exist.

Verified rather than eyeballed: heading counts and order match in both pairs,
every internal .md link resolves, every tool named in either README exists, and
every test in run_tests.sh appears in both.

Translating turned up four things that were already stale in the English, which
is the honest argument for having done it this way -- a summary would not have
touched them:

  - the endpoint table was missing /api/ptt, /api/power/<action> and
    /api/logs, and did not mention the speaker field on /api/status
  - the modelled-peripheral list omitted TIM2
  - the audit table still called TIM a stub, unchanged since fdcbe80 modelled
    TIM2
  - neither README listed uvk5_logs.py, uvk5_stream.py, uvk5_supervisor.py or
    test_kill_emulator.sh, which are part of the repo rather than scratch

The ad-hoc probe scripts are now acknowledged in one line instead of being
silently absent, and described as what they are: quick to reach for, not
polished.

Unit tests: 89 passed.

docs/reverse-proxy.md

@@ -3,6 +3,8 @@
 How `https://k6v3.mckero.dn42/` is set up on this host. The emulator UI itself
 speaks plain HTTP on loopback; nginx terminates TLS and proxies to it.
 
+*中文：[reverse-proxy.zh-CN.md](reverse-proxy.zh-CN.md) · the two are kept in step.*
+
 ## Why a proxy at all
 
 `tools/webui.py` has no TLS and no authentication. Running it on loopback and