improvement: refine HertzBeat AI tool guidance

[bigcyy]

Summary

Simplify and tighten the HertzBeat AI system prompt to make the assistant behavior clearer, more consistent, and easier to
maintain.

Why

The previous prompt contained duplicated guidance, overly detailed examples, and some outdated tool references. This made
it harder to keep tool usage instructions accurate as the AI tool interfaces evolved.

What Changed

• Reworked the system prompt into a more concise structure focused on operating principles and key workflows.
• Updated tool references to match the current tool names.
• Clarified guidance for monitor creation, alert rule creation, metrics queries, SOP skills, and scheduled tasks.
• Improved threshold expression guidance so alert rules preserve the user’s intended comparison direction.
• Updated skill README examples to use the current monitor query tool name.

Checklist

• I have read the Contributing Guide
• I have written the necessary doc or comment.
• I have added the necessary unit tests and all cases have passed.

Add or update API

• I have added the necessary e2e tests and all cases have passed.