Adds an informational `examples_overlay` field to SimulateResult,
populated from `summary_for_country` for the scenario's target country.
Never affects simulation paths — lookup failures are caught and logged,
yielding overlay=None. Wired into both /simulate and /compare; the
shared session in /compare is used sequentially because AsyncSession
is not safe for concurrent use.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>