bribe_circle_leader_cost

Gold cost the Emperor pays the leader when bribing a single circle. Also the per-member unit for scaling bribe_imperial_circle_target_cost (each non-leader member adds 25% on top). Scales with the Emperor's country_economical_base so the bribe stays meaningful as the Emperor grows — a flat baseline turned the action into pocket change once the imperial economy matured. References scope:actor explicitly because this value is also read inside scope:target = { ... } and every_circle_member sub-iterations (in both this file's bribe_imperial_circle_target_cost and in hre_circle_actions.txt's effect); without the explicit scope the inner reads would resolve against the wrong country.