feat: CrewAI framework adapter (shared ToolCapture)

[MarouaBoud]

Summary

Adds the CrewAI framework adapter, completing the "LangGraph / CrewAI adapters" delivery item (E19). Drive the swarm with your own CrewAI crew — stampede owns the population/target/chaos/report, your crew makes each tool decision (NG-3).

Stacked on #21 (the LangGraph adapter, which introduced frameworks.py). Merge #21 first; this PR auto-retargets to main when it does.

Design — a shared, tested capture

The key move: since CrewAI accepts LangChain tools (like LangGraph), both adapters share one capture path, refactored out of #21 into a ToolCapture helper:

• ToolCapture builds capture-stub tools (with arg schemas from the target spec), records calls, and yields the first as a decision — framework-agnostic and unit-tested.
• langgraph_agent_fn / crewai_agent_fn are now thin: each supplies only its one-line invocation (graph.ainvoke vs crew.kickoff).

So the CrewAI adapter's capture logic is verified, not write-blind — the same fake-driven test that covers LangGraph covers CrewAI (via langchain-core, no crewai install needed).

Config: population.framework: crewai + framework_ref: "module:crew_factory". New [crewai] extra.

Verified

• 141 tests pass, incl. a ToolCapture unit test and a CrewAI adapter test (name + args captured through a fake crew). ruff + mypy clean.
• examples/crewai_agent.py shows the crew_factory(tools, goal) a user writes.