docs: explain Claude prompt levels

[nicholasachow]

• Clarifies how each escalating prompt (“think” → “ultrathink”) increases Claude’s thinking budget
• Adds a reference to Anthropic’s official Claude Code Best Practices for deeper guidance

[Copilot]

Pull Request Overview

This PR adds documentation to explain Claude's escalating prompt levels and their effect on thinking budgets. It clarifies the hierarchy of prompts from "think" to "ultrathink" and references Anthropic's official best practices guide.

• Adds explanation of Claude's escalating prompt levels ("think" → "ultrathink")
• Includes reference to Anthropic's official Claude Code Best Practices documentation

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