docs: add copilot-instructions.md for better AI agent guidance

[saintedlama]

Extract existing coding patterns and styles to better guide AI agents when creating pull requests

[Copilot]

Pull Request Overview

This PR adds a comprehensive .github/copilot-instructions.md file to document coding patterns, styles, and conventions for better AI agent guidance when contributing to the Versionize project. The documentation extracts existing patterns from the codebase to establish consistent development standards.

• Creates a detailed guide covering C# language features, naming conventions, and code structure patterns
• Documents testing patterns using xUnit and Shouldly with specific naming and assertion conventions
• Provides configuration patterns, Git integration guidelines, and project structure organization

[coveralls]

Pull Request Test Coverage Report for Build 16466924743

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 92.73%

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Totals
Change from base Build 15103035361:	0.0%
Covered Lines:	1572
Relevant Lines:	1674

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💛 - Coveralls