feat(simulation): add tick rate scaling system

Replace binary paused flag with TickRate enum (Full/Half/Paused)
per D-052. Full rate advances every frame, Half every 2 frames
via fractional accumulation, Paused blocks all advances. Add
SetTickRate player action for client-driven rate changes.
Implements ticket #406.

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

server/src/knowledge/events.rs

@@ -260,7 +260,7 @@ mod tests {
         world.insert_resource(thresholds);
 
         // Tick 7: not a multiple of 10, decay should NOT run
-        world.insert_resource(SimulationTime { tick: 7, paused: false });
+        world.insert_resource({ let mut t = SimulationTime::default(); t.tick = 7; t });
         let mut schedule = bevy_ecs::schedule::Schedule::default();
         schedule.add_systems(decay_knowledge);
         schedule.run(&mut world);
@@ -273,7 +273,7 @@ mod tests {
         );
 
         // Tick 10: multiple of 10, decay SHOULD run (age = 10 > decay_after = 5)
-        world.insert_resource(SimulationTime { tick: 10, paused: false });
+        world.insert_resource({ let mut t = SimulationTime::default(); t.tick = 10; t });
         let mut schedule2 = bevy_ecs::schedule::Schedule::default();
         schedule2.add_systems(decay_knowledge);
         schedule2.run(&mut world);