docs: clarify Pi provider-prefixed model configuration

[Copilot]

Pi authentication is selected from the model: provider prefix, but Quick Start did not show complete values. Add concrete Copilot, Anthropic, and OpenAI examples.

• Quick Start
  • Extend Pi authentication guidance with valid provider-prefixed model values.

model: copilot/gpt-5.4
model: anthropic/claude-sonnet-5
model: openai/gpt-5

• Fixes [deep-report] Add concrete model: prefix example to Pi auth-resolution docs #55850

[github-actions]

Thanks for the documentation improvement! This PR clearly addresses the ambiguity in Pi's authentication configuration by adding concrete, real-world examples (Copilot, Anthropic, and OpenAI model prefixes) to the Quick Start guide.

The change is focused, well-described, and directly resolves #55850. This looks ready for review.

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[Copilot]

Pull request overview

Clarifies Pi authentication by adding complete provider-prefixed model examples.

Changes:

• Adds valid Copilot, Anthropic, and OpenAI model values.

Show a summary per file

File	Description
docs/src/content/docs/setup/quick-start.mdx	Adds concrete Pi model configuration examples.

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[github-actions]

🎉 This pull request is included in a new release.

Release: v0.87.8