NAI|NAVY_COMPARABILITY_RATIO

CCountry::HasAtLeastComparableNavyTo threshold. Replaces a strict-superiority navy check in the AI's cross-water reachability filter. 0.5 means a country with half the enemy's navy (or more) is still allowed to consider cross-water targets; the previous gate required strict superiority and was hiding Bosphorus-style strait crossings entirely.