DRAFT: parameter sensitivity analysis

_draft issue_
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Sensitivity analysis (SA) over parameters (probabilities and utilities) need to be implemented.
SA can be:
- One parameter at a time
- Looping over all (or selected subset) parameters (one at a time)
- All (or a selected subset) parameters simultaneously

This means
- Updating the front end for allowing the selection of variables to investigate
- Updating the front end for allowing the input of investigated ranges for the selected variables
- Updating the DB for tracking SA setup
- Updating the back end for computations
- Updating the front end for visualization and documentation of the SA results

No files, tests, or entry points are named, so first clarify the sensitivity-analysis design and locate the frontend, database, and backend areas involved. Done would include parameter selection and ranges, stored SA setup, backend computations, and frontend visualization and documentation for the results.

Written by the indexing model from the issue text.