Add CrewAI integration + CLI for standalone running

- OpusCrew base class with CrewAI LLM integration
- FictionCrew: Writer, Editor, Proofreader agents
- NonfictionCrew: Researcher, Writer, Fact-Checker, Editor agents
- CLI entry point: python -m opus_orchestrator
- Commands: generate, frameworks, config
- Test: generated 282-word story with CrewAI crews

Usage:
    python -m opus_orchestrator generate --concept 'Your idea' --use-crewai
    python -m opus_orchestrator frameworks
    python -m opus_orchestrator config

opus_orchestrator/__main__.py

@@ -0,0 +1,7 @@
+"""CLI entry point for Opus Orchestrator."""
+
+from opus_orchestrator.cli import main
+
+if __name__ == "__main__":
+    import sys
+    sys.exit(main())