Add repository-level Copilot coding instructions

[Copilot]

This issue requested repository-specific Copilot guidance aligned with GitHub’s coding-agent best practices. This PR adds a single authoritative instruction file so agent behavior is consistent with FreeThinker’s architecture and platform constraints.

• What was added

  • Created .github/copilot-instructions.md as the repo-level instruction source for Copilot coding agents.

• Instruction scope

  • Captures core project context (Swift 5.9+, SwiftUI/AppKit, FoundationModels, module boundaries).
  • Defines coding expectations (minimal/safe edits, reuse existing abstractions, preserve async/actor patterns).
  • Documents validation commands and macOS-specific build note (-skipMacroValidation).
  • Reinforces platform constraints (macOS 26+, Apple Silicon, on-device AI only).

• Resulting repo contract

  • Establishes a concise, discoverable policy file for future automated and assisted code changes without touching app/runtime code paths.

# Copilot instructions for FreeThinker

## Project context
- FreeThinker is a macOS menu bar app built with Swift 5.9+, SwiftUI, and AppKit.
- The app is local-first and uses Apple FoundationModels (`SystemLanguageModel`) for on-device AI.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• gh.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>✨ Set up Copilot instructions</issue_title>
<issue_description>Configure instructions for this repository as documented in Best practices for Copilot coding agent in your repository.

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes ✨ Set up Copilot instructions #17

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

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