🩹 [Patch]: Create comprehensive GitHub Copilot instruction file

[Copilot]

This PR adds a comprehensive GitHub Copilot instruction file to help contributors and users better understand the Process-PSModule framework conventions, coding standards, and project structure.

What was added

Created .github/copilot-instructions.md with detailed guidance covering:

Repository Understanding

• Process-PSModule overview - Purpose as a reusable workflow for PowerShell module development
• Workflow pipeline - 11-stage CI/CD process from settings to publishing
• Multi-OS testing - Linux, macOS, Windows support with matrix strategies

PowerShell Development Standards

• Code structure - Standard directory layout (src/functions/public/, src/functions/private/, etc.)
• Function patterns - Complete template with comment-based help, parameters, and error handling
• Code style - Based on PSScriptAnalyzer configuration (4-space indent, 150-char lines, bracing style)

Testing & Quality

• Pester test structure - Arrange/Act/Assert patterns with proper context organization
• Test file organization - Unit vs integration tests, naming conventions
• Code coverage - Target requirements and reporting

Documentation & Configuration

• Comment-based help - Required sections (.SYNOPSIS, .DESCRIPTION, .PARAMETER, .EXAMPLE)
• PSModule.yml configuration - Complete structure with skip options and publishing settings
• Markdown documentation - Standards for function and project documentation

Development Patterns

• Module requirements - #Requires statements for dependencies
• Alias definitions - Multiple supported patterns for function aliases
• PSScriptAnalyzer suppressions - Proper format with justifications
• Parameter validation - Common validation patterns and attributes

Workflow Integration

• GitHub Actions patterns - Input/output structure, secrets management
• Conditional execution - How tests and builds are skipped based on configuration
• Publishing flow - PowerShell Gallery and GitHub Pages deployment

Benefits for Contributors

This instruction file will enable GitHub Copilot to:

• Generate PowerShell functions following PSModule framework conventions
• Create proper Pester tests with correct structure and organization
• Suggest appropriate documentation and comment-based help
• Understand the build/test/publish workflow requirements
• Follow established coding standards automatically
• Provide context-aware suggestions for configuration files

The 973-word instruction file with 22 detailed sections provides comprehensive coverage of all aspects needed for successful contribution to PowerShell modules using the PSModule framework.

Fixes #178.

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