docs: add a coding-agent guide for Vite+ command usage

[crusty-voidzero]

Summary

Follow up on recent AI-assisted Vite+ usage: we should document more clearly how coding agents should invoke Vite+ commands, especially when forwarding args to scaffolding/templates.

Problem

We saw an AI workflow pass extra args to Vite+ incorrectly.

Today the docs mention vp create <template> -- <template-options> and include a few migration-agent notes, but there is no single page we can point coding agents to for Vite+ command conventions and common gotchas.

Proposed docs work

• Add a dedicated docs page for coding agents / AI-assisted Vite+ workflows
• Explain when to use -- to forward args to templates or underlying tools
• Show a few canonical examples, e.g.:
  • vp create vite -- --template react-ts
  • other representative forwarding cases if we support them
• Call out common mistakes explicitly (for example: passing template args directly to vp create without --)
• Link to this page from the existing create/migrate/agent-related docs so Codex and other agents have an obvious source of truth

Acceptance criteria

• A dedicated docs page exists and is linked from the relevant Vite+ docs
• The page includes concrete command examples and a short “common mistakes” section
• The guidance is clear enough that we can point coding agents to it directly

Notes

This is intended as a docs follow-up, not a product behavior change.