docs(rfc): split manager runtime profile into a Chinese mirror

[huangruiteng]

Purpose

Fix the red nightly docs-governance-smoke on main. It fails with
RFC missing required Chinese mirror: manager-runtime-profile-v0.md, not because the
content lacks Chinese, but because #4337 landed the RFC in the legacy in-file
## 中文 / ## English layout. The RFC template requires new RFCs to ship
<same-basename>.zh-CN.md with reciprocal language links in both documents, and the
allowlist comment explicitly asks not to weaken that invariant.

Changed surfaces

• docs/architecture/rfcs/manager-runtime-profile-v0.md: English document plus the standard
  semantic-mirror note linking the Chinese file.
• docs/architecture/rfcs/manager-runtime-profile-v0.zh-CN.md: new Chinese mirror with the
  reciprocal link and 语义镜像 note.
• No runtime, configuration, capability catalog, or documentation-pointer change: the
  manager_runtime capability documentation path stays on the English RFC.

Content preservation

The split is mechanical, not a retranslation. Verified against HEAD before the change:

• the English body is byte-identical to the previous ## English section;
• the Chinese body is byte-identical to the previous ## 中文 section;
• only the header blocks (title, status line, language note) are new.

Validation

• examples/docs-governance-smoke.py: docs-governance-smoke ok on this head. It failed on
  the same base with the missing-mirror assertion before the change.
• python -m pytest tests/test_chat_machine_configuration_api.py -q: 12 passed (guards the
  capability documentation pointer that references this RFC).
• Cross-links resolve under assert_local_doc_links_resolve.

Merge note

Documentation-only, single-purpose and reversible by restoring the single-file layout.
Bypass approval is required because the author cannot approve their own pull request.