AGENTS.md should mention CI integration

[Justineo]

Description

LLMs don’t yet have knowledge of voidzero-dev/setup-vp from their pretraining data and coding agents are generating traditional Node, package-manager, and cache setup.

Suggested solution

We should document voidzero-dev/setup-vp in the scaffolded AGENTS.md to help coding agents configure CI more smoothly.

Alternative

No response

Additional context

No response

Validations

• Read the Contributing Guidelines.
• Confirm this request is for Vite+ itself and not for Vite, Vitest, tsdown, Rolldown, or Oxc.
• Check that there isn't already an issue requesting the same feature.