chore: Add AGENTS.md

[FrederikBolding]

Add AGENTS.md file with instructions for AI agents that operate on the repository. The goal is to outline our requirements for feature development and any quirks in using the repo.

Mostly written by Claude as an experiment, but with edits and guidance from myself. Also with inspiration from MetaMask/core#7765

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Note

Low Risk
Low risk: documentation-only addition plus a small lint-staged pattern tweak that only affects formatting behavior for CLAUDE.md. No runtime or package code changes.

Overview
Adds AGENTS.md, a repository guide for AI coding agents covering stack/tooling, monorepo conventions, build/test/lint commands, changelog requirements, and high-level Snaps platform architecture/naming guidelines.

Adds CLAUDE.md pointing to AGENTS.md, and updates lint-staged in package.json to exclude CLAUDE.md (alongside CHANGELOG.md) from Prettier formatting.

^{Written by Cursor Bugbot for commit 4ade350. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.39%. Comparing base (54d632d) to head (4ade350).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3823   +/-   ##
=======================================
  Coverage   98.39%   98.39%           
=======================================
  Files         430      430           
  Lines       12454    12454           
  Branches     1936     1936           
=======================================
  Hits        12254    12254           
  Misses        200      200           

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