Add GitHub MCP server to OpenCode configuration

[Copilot]

Test issue for validating GitHub Copilot integration with MCP servers. Adds GitHub MCP server configuration to complete the test.

Changes

• opencode.json: Added GitHub MCP server using @modelcontextprotocol/server-github

  "github": {
    "type": "local",
    "command": ["npx", "-y", "@modelcontextprotocol/server-github"],
    "enabled": true
  }

• README.md: Added MCP server configuration section documenting all four servers (Sequential Thinking, Context7, Serena, GitHub) in config file order

• MCP_INTEGRATION_TEST.md: Test documentation showing successful integration verification

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Test] Copilot MCP 연동 테스트</issue_title>
<issue_description>GitHub MCP Server + Copilot 연동 테스트용 이슈입니다.

테스트 완료 후 닫을 예정.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Test] Copilot MCP 연동 테스트 #1

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.