Generate Copilot Instructions

[scottluskcis]

Generate a copilot-instructions file in the .github folder. Look at the existing README in the root for guidance.

This should outline

• how we build and code goes in src folder
• how we test using vitest and tests go in tests folder
• recommend we follow SOLID design patterns
• anytime we make changes make sure pnpm ci runs successfully
• always check linting and formatting before running ci
• when adding new features put a doc in the docs folder
• any other details we can gather about the project
• copilot review will run on PRs