feat(researcher): DCE-MRI BBB permeability bridge + drug-dose adjuster

feat(api): add POST /fusion/predict route for multi-modal fusion

feat(agents): live OpenRouter integration test (slow) + GET /diag/agent

feat(api): POST /agent/run endpoint (orchestrator + RAG, stub-injectable)

chore(diag): add /diag/openrouter endpoint + sidebar button

feat(api): GET /experiments/runs + POST /experiments/diff (Track 5)

feat(api): POST /explain/bbb — natural-language rationale endpoint

feat(api): POST /predict/bbb with prediction, uncertainty, SHAP top-k

feat(api): POST /pipeline/{bbb,eeg,mri} dispatch routes

feat(api): scaffold FastAPI app + /health + shared Pydantic schemas