Document tracker compatibility and size priorities for agents

[simple-analytics-ai]

Summary

Fixes #114

Record the tracker priorities agreed during the v12 compatibility and inline-event reviews. This branch starts from and targets v12.

 AGENTS.md
- hardcoded Node/npm commands and blanket test instructions
+ shared guidance and eight tracker-specific rules

The rules cover measured minified/gzip size, existing customer behavior, simple implementations, native website interactions, collection controls, browser/build compatibility, focused validation, and small PRs.

Evidence

• Before: The guide required Node 22.16, npm commands, and a missing test:unit script while omitting recurring tracker requirements.
  After: Runtime and command details come from repository configuration; numbered rules capture the agreed requirements.
• Only AGENTS.md changes. Tracker source, generated assets, dependencies, and workflows are unchanged.

Security implications

• No security impact
• Has security impact - described as:

Testing

• Prettier 2.8.8: --check AGENTS.md passed using the repository configuration.
• git diff --check passed.
• Reviewed against the shared instructions and the agreed scope. Runtime tests and BrowserStack were not run for this documentation-only change.

Merge Danger

Door: two-way

Blast Radius: Agents

Changes future agent guidance; reverting restores the previous instructions.

Checklist

• Linked to an issue
• Tested
• Asked for a review

[github-actions]

Claude review checkpoint

Reviewed commit 04d7aee397663c4c5e1da24500ba07e7700794a6. This is used to keep later automated reviews focused on changes Claude has not checked yet.

[github-actions]

SDLC label: change: routine because Documentation-only edit to internal agent guidance in AGENTS.md; no tracker source, generated output, dependencies, workflows, data collection, auth, billing, or infrastructure behavior changes