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

fix(frontend): toast icon must be valid emoji, not ✓

fix(frontend): EEG default path points at fixture (HF container has no data/raw/eeg.fif)

feat(frontend): premium motion layer — Apple HIG / Netflix transitions

feat(frontend): editorial redesign — neutral-gray dark + sand accent + dual theme

feat(frontend): Experiments tab — MLflow runs table + two-run diff

feat(frontend): inline AI Assistant in EEG + MRI tabs

feat(frontend): AI Assistant tab — natural-language explainer

feat(api+frontend): MLflow provenance badge in decision card

feat(frontend): drift metric line + last-prediction session state

feat(frontend): MRI tab — Pre/Post ComBat KDE + site-gap KPI strip

feat(frontend): trust caption — precision-at-confidence below decision card

feat(frontend): edge-case dropdown for BBB robustness demo

feat(frontend): interactive BBB tab — SMILES input + decision card + SHAP bars

feat(frontend): Streamlit dashboard with 3 modality tabs