✨ Set up Copilot instructions and EditorConfig

.editorconfig

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+# EditorConfig is awesome: https://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+# Unix-style newlines with a newline ending every file
+[*]
+end_of_line = lf
+insert_final_newline = true
+charset = utf-8
+trim_trailing_whitespace = true
+
+# Bash scripts
+[bin/m]
+indent_style = space
+indent_size = 2
+
+# Markdown files
+[*.md]
+indent_style = space
+indent_size = 2
+# Don't enforce max line length in markdown (especially for tables, code blocks)
+max_line_length = off
+
+# JSON files
+[*.json]
+indent_style = space
+indent_size = 2
+
+# YAML files
+[*.{yml,yaml}]
+indent_style = space
+indent_size = 2
+
+# JavaScript/Node.js files
+[*.{js,mjs}]
+indent_style = space
+indent_size = 2

.github/instructions/README.md

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+# Copilot Instructions
+
+This directory contains instructions for GitHub Copilot and other AI coding assistants to help maintain code quality and consistency in this repository.
+
+## Instruction Files
+
+Each instruction file includes a YAML frontmatter section that specifies which files the instructions apply to using glob patterns.
+
+### `general.instructions.md`
+**Applies to**: `**/*` (all files)
+
+Provides general context about the project:
+- Project overview and characteristics
+- Core development principles
+- Guidelines for code changes, documentation, and testing
+- File organization
+- Safety and security practices
+
+### `m.instructions.md`
+**Applies to**: `bin/m` (main Bash script)
+
+Detailed guidelines for the main Bash executable:
+- Style and formatting conventions
+- Logging and error handling patterns
+- CLI/dispatch conventions
+- Version and regex handling
+- Networking and downloads
+- OS/distro/arch detection
+- Filesystem operations and hooks
+- Safety and portability checks
+- Quick review checklist
+
+### `docs.instructions.md`
+**Applies to**: `/**/*.md` (all Markdown files)
+
+Documentation-specific guidelines:
+- Focus on clarity and accuracy
+- Maintain consistency with `.editorconfig` settings
+- Special handling for tables, code blocks, and frontmatter
+
+## Related Files
+
+### `.editorconfig`
+Defines code formatting standards for various file types in the repository. The documentation instructions reference this file to ensure consistency.
+
+## How It Works
+
+When GitHub Copilot or similar AI assistants work on files in this repository, they automatically read and apply the relevant instructions based on the `applyTo` patterns. This helps ensure:
+
+1. **Consistency**: All changes follow established patterns
+2. **Safety**: Critical checks and validations are not bypassed
+3. **Quality**: Code reviews catch common issues
+4. **Context**: AI has necessary background about the project
+
+## Maintaining Instructions
+
+When updating these instructions:
+1. Keep the YAML frontmatter with `applyTo` patterns
+2. Be specific and actionable
+3. Include examples where helpful
+4. Test that the instructions improve code quality
+5. Keep them focused on guidance that can be applied programmatically
+
+## References
+
+- [GitHub Copilot Instructions Documentation](https://gh.io/copilot-coding-agent-tips)
+- [EditorConfig Specification](https://editorconfig.org)

.github/instructions/general.instructions.md

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+---
+applyTo: "**/*"
+---
+
+# General Instructions for m Repository
+
+## About the Project
+
+`m` is a MongoDB version management tool written in Bash. It helps users download, install, and manage multiple versions of MongoDB server and command-line tools.
+
+## Key Characteristics
+
+- **Primary Language**: Bash scripting (bin/m is the main executable)
+- **Cross-platform**: Supports Linux and macOS (including Apple Silicon)
+- **Package Manager**: Distributed via npm but implemented as a Bash script
+- **Testing**: Node.js-based test suite (test/suite.mjs)
+
+## Core Principles
+
+1. **Minimal Dependencies**: The tool should work with standard Unix utilities and Bash
+2. **Cross-platform Compatibility**: Changes must work on both Linux and macOS
+3. **Backward Compatibility**: Preserve existing behavior and CLI interface
+4. **Safety First**: Handle errors gracefully, validate inputs, and clean up on failures
+
+## Development Guidelines
+
+### Code Changes
+
+- Follow existing code style and conventions (see file-specific instructions)
+- Test on both Linux and macOS when possible
+- Ensure all existing tests pass before submitting changes
+- Add tests for new functionality when appropriate
+
+### Documentation
+
+- Keep README.md up to date with CLI changes
+- Use clear, concise language suitable for technical users
+- Include examples for new features
+- Follow the existing documentation structure and tone
+
+### Testing
+
+- Run the test suite with `npm test` before submitting changes
+- Test manually with actual MongoDB downloads when modifying installation logic
+- Verify cross-platform behavior for platform-specific changes
+
+## File Organization
+
+- `bin/m` - Main Bash executable
+- `test/` - Node.js test suite
+- `.github/instructions/` - Copilot AI instructions for code review
+- `README.md` - User-facing documentation
+- `CONTRIBUTING.md` - Contribution guidelines
+
+## Common Tasks
+
+- **Version Bumping**: Update VERSION variable in bin/m and version in package.json
+- **Adding CLI Commands**: Update help text, case statement, and add tests
+- **Documentation Updates**: Keep README.md in sync with code changes
+
+## Safety and Security
+
+- Never expose credentials or API tokens
+- Validate all user inputs
+- Use quotes around variables to prevent word splitting issues
+- Clean up temporary files and directories on failure
+- Check exit codes and handle errors appropriately