feat(agents): register run_fusion tool for multi-modal disease confidence

fix(agents/orchestrator): log dropped out-of-stage tool calls (was silent)

docs(agents/tools): TODO race on shared parquet output for concurrent /agent/run

Add project files

fix(agents/tools): parameterize processed_dir + translate HTTPException → ValueError

feat(agents): orchestrator loop (function-calling + tool trace + max-steps gate)

feat(agents): Tool dataclass + registry + 4 tool wrappers (3 pipelines + RAG)