docs: update Learning Hub for Copilot CLI v1.0.61-v1.0.64 (#2119)

- understanding-mcp-servers: add .github/mcp.json to config discovery table (v1.0.61)
- installing-and-using-plugins: add extensions as a plugin component type (v1.0.62)
- copilot-configuration-basics: add /settings, /worktree, and /diagnose commands (v1.0.61, v1.0.64); note per-model token totals in /usage (v1.0.64)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

website/src/content/docs/learning-hub/understanding-mcp-servers.md

@@ -3,7 +3,7 @@ title: 'Understanding MCP Servers'
 description: 'Learn how Model Context Protocol servers extend GitHub Copilot with access to external tools, databases, and APIs.'
 authors:
   - GitHub Copilot Learning Hub Team
-lastUpdated: 2026-06-23
+lastUpdated: 2026-06-24
 estimatedReadingTime: '8 minutes'
 tags:
   - mcp
@@ -66,6 +66,7 @@ MCP servers are configured per-workspace. GitHub Copilot CLI discovers server de
 | File | Scope | Notes |
 |------|-------|-------|
 | `.mcp.json` | Repository root | Preferred for repo-shared configuration |
+| `.github/mcp.json` | Repository `.github/` folder | Auto-loaded workspace config (v1.0.61+) |
 | `.vscode/mcp.json` | VS Code workspace | VS Code–compatible workspace config |
 | `devcontainer.json` | Dev container | Available when running inside a container |