docs: add missing LLM Agent installation step links to translated READMEs ToC (#458)

- Update README.ko.md ToC with Korean step links
- Update README.ja.md ToC with Japanese step links
- Update README.zh-cn.md ToC with Chinese step links

These ToC links were present in README.md (English) but missing
from the translated versions, making navigation inconsistent.

Fixes #457

Co-authored-by: sisyphus-dev-ai <sisyphus-dev-ai@users.noreply.github.com>

README.zh-cn.md

@@ -82,6 +82,19 @@
   - [安装](#安装)
     - [人类专用](#人类专用)
     - [给 LLM Agent 看的](#给-llm-agent-看的)
+    - [步骤 0：确认订阅情况](#步骤-0确认订阅情况)
+    - [步骤 1：确认 OpenCode 装没装](#步骤-1确认-opencode-装没装)
+    - [步骤 2：跑安装程序](#步骤-2跑安装程序)
+    - [步骤 3：验货](#步骤-3验货)
+    - [步骤 4：搞定认证](#步骤-4搞定认证)
+      - [4.1 Anthropic (Claude)](#41-anthropic-claude)
+      - [4.2 Google Gemini (Antigravity OAuth)](#42-google-gemini-antigravity-oauth)
+      - [4.3 OpenAI (ChatGPT Plus/Pro)](#43-openai-chatgpt-pluspro)
+    - [⚠️ 注意](#️-注意)
+    - [检查作业](#检查作业)
+    - [跟用户说"恭喜！🎉"](#跟用户说恭喜)
+    - [太麻烦了？](#太麻烦了)
+  - [卸载](#卸载)
   - [功能](#功能)
     - [Agents：你的神队友](#agents你的神队友)
     - [后台 Agent：像真正的团队一样干活](#后台-agent像真正的团队一样干活)