Add flexibility around server instructions for search-related tools

[tommaso-moro]

Make search-related instructions more flexible, for consistency with remote server

[Copilot]

Pull Request Overview

This PR updates the GitHub MCP Server instructions to make search-related tool guidance more flexible and consistent with a remote server implementation. The changes reorganize the instruction text and modify the guidance for search tools to be more generic.

• Simplified the opening description from "GitHub platform" to just "GitHub"
• Reorganized instruction sections to put context management before tool selection guidance
• Updated search tool guidance to reference any tools containing 'search' in their name rather than specifically 'search_*' tools

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