feat(notebook): add agents handoffs cookbook with multi-agent routing

[abdelhadi703]

Description

Adds a Jupyter notebook demonstrating Mistral's Agents API handoff capabilities. The cookbook currently has Chainlit-based agent examples (travel_assistant, food_diet_companion) but no .ipynb notebook covering handoffs — this fills that gap.

Content

• Simple handoff: Triage agent routing queries to a Code Expert (code_interpreter) and a Research Expert (web_search)
• Server mode: Automatic handoff execution with real-time SSE event handling (AgentHandoffStartedEvent, AgentHandoffDoneEvent)
• Client mode: Manual handoff routing with handoff_execution="client" for custom control flow
• Multi-agent network: Travel assistant pattern with 4 agents (triage + flights + hotels + activities) and cross-handoffs via agents.update()
• Conversation history: Inspecting AgentHandoffEntry via get_history()
• Cleanup: Proper agent deletion

Conventions

• API key via os.environ with getpass fallback (no hardcoded keys)
• Pinned SDK version (mistralai>=1.6.0)
• Colab badge at the top
• Clean cell outputs
• All API calls verified against the mistralai Python SDK v1.10.0 signatures

Testing

• Notebook JSON is valid
• All API method names and parameters verified against SDK source
• Event types (AgentHandoffStartedEvent, AgentHandoffDoneEvent, MessageOutputEvent) match SDK definitions
• End-to-end run with API key (requires live API access)

[abdelhadi703]

Hi @mistralai/team,

Gentle reminder on this multi-agent routing cookbook. It shows how to implement agent handoffs with Mistral.

Happy to make adjustments based on review. Thanks!