fix(backend): post-review fixes sprint 2

- test_simulations_patch: remove false dict return annotation on _patch helper
- simulation_workflow: validate executed_at upfront before any setattr (prevents partial mutation on bad payload)
- api/simulations: remove unreachable role check in update_simulation (all valid roles are admin/redteam/soc)
- Dockerfile: remove redundant COPY backend/data/ (already covered by COPY backend/)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker/Dockerfile

@@ -12,7 +12,6 @@ WORKDIR /app
 COPY backend/requirements.txt ./backend/
 RUN pip install --no-cache-dir -r backend/requirements.txt
 COPY backend/ ./backend/
-COPY backend/data/ ./backend/data/
 COPY --from=frontend-build /app/frontend/dist ./backend/app/static
 
 ENV FLASK_APP=backend.app:create_app