Add comprehensive Copilot instructions for SourceMod plugin development

[Copilot]

This PR onboards the repository to GitHub Copilot coding agent by adding a comprehensive .github/copilot-instructions.md file. The instructions provide essential context for coding agents to work efficiently with this SourceMod plugin repository.

What's Added

The new instructions file includes:

• Repository Overview: Clear description of the VIP SourceMod Flags plugin's purpose and functionality for managing VIP user permissions
• Technical Environment: Complete setup information including SourcePawn language, SourceMod 1.11+ platform, and SourceKnight build system
• Dependencies: Detailed mapping of all required and optional dependencies with their purposes:
  • Required: sourcemod, vip_core, multicolors, utilshelper
  • Optional: ccc (Custom Chat Colors), sourcebanspp (SourceBans++)
• Code Style & Standards: SourcePawn-specific conventions including indentation, naming patterns, memory management, and pragma requirements
• Plugin Architecture: Explanation of core components, key functions (LoadVIPClient, UnloadVIPClient), and configuration variables
• Development Guidelines: Best practices for adding features, testing procedures, and integration patterns
• Common Tasks: Code examples for typical development activities like adding ConVars and admin commands
• Build System: Complete documentation of SourceKnight configuration and CI/CD pipeline
• Troubleshooting: Debugging tips and common issue resolution strategies

Why This Matters

This documentation will significantly improve the quality of AI-assisted development by providing:

• Context about the plugin's role in the VIP system ecosystem
• Understanding of SourceMod's event-driven architecture
• Knowledge of proper memory management and performance considerations
• Awareness of integration points with other plugins
• Clear guidance on testing and validation procedures

The instructions are specifically tailored to this repository's codebase and follow established SourcePawn development patterns found in the existing code.

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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.