Add CI pipeline with Prettier formatting check

[Copilot]

Adds a minimal GitHub Actions workflow that enforces Prettier formatting on push to main and on PRs.

• CI workflow (.github/workflows/ci.yml): Sets up Bun, installs deps with frozen lockfile, runs prettier --check .
• Prettier dependency: Added prettier@3.5.3 to devDependencies and format:check script to package.json
• Existing formatting fix: Ran Prettier on docs/adr-001-react-effect.md so CI passes on merge

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:

• https://api.github.com/repos/Jarred-Sumner/bun-releases-for-updater/releases/latest
  • Triggering command: /home/REDACTED/.bun/bin/bun bun upgrade (http 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

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This section details on the original issue you should resolve

<issue_title>There is no CI pipeline</issue_title>
<issue_description>There should be a minimal GitHub Action that checks if files are formatted correctly (according to Prettier).</issue_description>

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

• Fixes There is no CI pipeline #1

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