fix(preflight): resolve registered workflow profile APIs

[wisdom-pan]

Summary

• Resolve public pipeline IDs to their actual workflow profile modules.
• Use the current ReAct and Agent Team profile loader and builder APIs.
• Return clean diagnostics when LLM client construction fails instead of raising a traceback.
• Add regression tests for both built-in workflows and invalid pipeline handling.

Problem

The documented default preflight treated the public pipeline ID stateful-react-agent as an importable Python package name, although the implementation lives in workflows.stateful_react_agent. It also called the retired generic load_profile and create_llm APIs, so both built-in workflow checks failed before making the intended one-token validation request.

Validation

• 1729 tests passed
• Ruff passed
• Pyright passed
• Framework and eval import smoke checks passed
• Symbol and lazy-export checks passed
• Stateful ReAct and Agent Team verified against the bundled mock endpoint