docs(#743): address Kimi review — runtime count + support boundary

Address remaining review feedback on PR #743:

- Bump supported-runtime count 15 -> 16 across user-facing READMEs
  (docs/README.md + ja-JP/zh-CN translations) now that Kimi is added.
- Add an explicit support-boundary note in the Kimi CLI install section:
  the kimi --agent-file custom-agent contract targets legacy/Python
  kimi-cli; newer npm Kimi Code (@moonshot-ai/kimi-code) rejects
  --agent-file and consumes the same /skill:gsd-* skills via --skills-dir.
- Mirror the boundary in the changeset so release notes are unambiguous.

Historical ADR/changeset/INVENTORY references to '15 runtimes' are left
intact as point-in-time records.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/how-to/install-on-your-runtime.md

@@ -214,6 +214,8 @@ All registered hooks are managed by GSD and are removed cleanly on `--uninstall`
 
 ### Kimi CLI
 
+> **Support boundary — legacy `kimi-cli` vs Kimi Code.** This integration targets the legacy/Python `kimi-cli` custom-agent contract. The `kimi --agent-file <configRoot>/agents/gsd.yaml` launch shown below is accepted by `kimi-cli`. The newer npm Kimi Code (`@moonshot-ai/kimi-code`, e.g. `0.11.0`) does **not** accept `--agent-file`; it discovers skills through fixed skill roots and `--skills-dir`. The generated `/skill:gsd-*` skills work in both, but the custom-agent (`--agent-file`) surface is specific to legacy `kimi-cli`. For Kimi Code, point it at the installed skills root with `--skills-dir <configRoot>/skills` instead of using `--agent-file`.
+
 ```bash
 npx @opengsd/gsd-core@latest --kimi --global
 ```