Add four high-priority articles identified by gap analysis against
nishanil/copilot-guide:
- Building Custom Agents: personas, tools, MCP integration, patterns
- Understanding MCP Servers: what MCP is, configuration, agent usage
- Automating with Hooks: lifecycle events, hooks.json, practical examples
- Using the Copilot Coding Agent: setup steps, issue assignment, PR workflow
Update index.astro fundamentalsOrder to include all 10 articles.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>