feat(notebook): add reasoning capabilities cookbook

[abdelhadi703]

Summary

Add a new cookbook notebook demonstrating Mistral's reasoning capabilities using the Magistral models (magistral-small-latest, magistral-medium-latest).

The cookbook currently has no notebook dedicated to reasoning or chain-of-thought prompting. This notebook fills that gap by providing practical, runnable examples.

What's included

• Thinking traces parsing: How to separate thinking blocks from text blocks in Magistral responses
• Chain-of-thought prompting: Explicit CoT instructions for complex multi-step problems
• Mathematical reasoning: Train meeting problems, algebraic equations
• Logical deduction: Classic truth-teller/liar puzzles
• Code analysis: Bug detection and correction with step-by-step reasoning
• Reasoning vs. standard comparison: Side-by-side comparison of magistral-medium-latest vs mistral-large-latest on the same problem
• prompt_mode parameter: How to control reasoning behavior with custom system prompts
• Real-world scenario: Project planning with critical path analysis

Technical details

• Uses mistralai==1.12.4 (pinned version)
• No hardcoded API keys (os.environ.get("MISTRAL_API_KEY"))
• Runnable on Google Colab (badge included)
• Clean outputs (no cell outputs committed)
• Follows existing cookbook format (modeled after prompting_capabilities.ipynb)

Files changed

• mistral/reasoning/reasoning_capabilities.ipynb (new)
• README.md (added entry to Main Notebooks table)

[abdelhadi703]

Hi @mistralai/team,

Bumping this PR for review. It adds a practical notebook demonstrating reasoning capabilities with Mistral models.

Let me know if you'd like any changes. Thanks!