Add development guidelines for minimal file changes to Copilot instructions

[Copilot]

Plan: Update Copilot Custom Instructions

• Analyze current copilot instructions in .github/copilot-instructions.md
• Review the repository structure and build process
• Validate that build and lint processes work correctly
• Add instruction about making minimal changes to only necessary files
• Test the changes by running build/lint again
• Verify the updated instructions are clear and actionable
• Remove package-lock.json changes from changeset as requested

Changes Made

Added a new Development Guidelines section to .github/copilot-instructions.md with three key principles:

1. Minimal Changes: Only modify files directly needed for the actual changes being implemented
2. Focused Modifications: Make surgical, precise changes that address specific requirements
3. Preserve Existing Structure: Maintain existing code organization and file structure

The new guidelines emphasize avoiding unnecessary changes to unrelated files, configuration files, or dependencies unless absolutely essential for the task. This ensures that code changes remain focused and minimize the risk of introducing unintended side effects.

Removed the package-lock.json changes that were inadvertently included when dependencies were installed during development. The changeset now only includes the intended documentation update to .github/copilot-instructions.md.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Update Copilot custom instructions</issue_title>
<issue_description>Add the instruction to only change files that are needed for the actual changes, and not to touch any other file.</issue_description>

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

Fixes #12

---

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

[rajbos]

@copilot remove the package lock file from the changeset

[Copilot]

@copilot remove the package lock file from the changeset

Done! I've removed the package-lock.json changes from the changeset (commit 295968c). The PR now only includes the intended documentation update to .github/copilot-instructions.md.

[rajbos]

LGTM