docs(agents): convert install shell snippets to markdown refs

agents/install-cli.md

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+# Agent CLI Commands
+
+Reference commands for installing and updating agent CLIs. Run only the commands you need.
+
+## Install CLIs
+
+```bash
+# codex
+npm i -g @openai/codex
+
+# opencode
+npm install -g opencode-ai
+
+# kimi-cli
+uv tool install --python 3.13 kimi-cli
+uv tool upgrade kimi-cli --no-cache
+
+# gemini-cli
+npm install -g @google/gemini-cli
+```
+
+## Optional tooling
+
+```bash
+# context7: up-to-date docs and code examples for LLMs and agents
+npx ctx7 setup
+```
+
+## Update npm-installed agent tools
+
+```bash
+npm update -g
+```