chore: import upstream snapshot with attribution

docs/guide/installation.md

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+# Installation
+
+## Requirements
+
+- **Node.js**: >= 21.0.0, or **Bun** >= 1.0
+- **Chrome** running and logged into the target site (for browser commands)
+
+## Install via npm (Recommended)
+
+```bash
+npm install -g @jackwener/opencli
+```
+
+## Install from Source
+
+```bash
+git clone git@github.com:jackwener/opencli.git
+cd opencli
+npm install
+npm run build
+npm link      # Link binary globally
+opencli list  # Now you can use it anywhere!
+```
+
+## Update
+
+```bash
+npm install -g @jackwener/opencli@latest
+
+# If you use the packaged OpenCLI skills, refresh them too
+npx skills add jackwener/opencli
+```
+
+Or refresh only the skills you actually use:
+
+```bash
+npx skills add jackwener/opencli --skill opencli-adapter-author
+npx skills add jackwener/opencli --skill opencli-autofix
+npx skills add jackwener/opencli --skill opencli-browser
+npx skills add jackwener/opencli --skill opencli-browser-sitemap
+npx skills add jackwener/opencli --skill opencli-sitemap-author
+npx skills add jackwener/opencli --skill opencli-usage
+npx skills add jackwener/opencli --skill smart-search
+```
+
+## Verify Installation
+
+```bash
+opencli --version   # Check version
+opencli list        # List all commands
+opencli doctor      # Diagnose connectivity
+```