test(server): add Entity::to_bits roundtrip and TickRate switch tests

- Entity::to_bits() roundtrip test guards against bevy version changes
  silently breaking wire IDs (Hoshe #1)
- PROTOCOL_VERSION constant used in test helpers instead of hardcoded 4
- TickRate switch mid-accumulation test verifies Half→Full→Paused→Half
  transitions preserve accumulator state correctly (Tyre N3)
- POI mid-range test now asserts priority=1 (Hoshe #4)

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

server/src/simulation/time.rs

@@ -199,6 +199,37 @@ mod tests {
         assert_eq!(time.day(), 3);
     }
 
+    #[test]
+    fn tick_rate_switch_mid_accumulation() {
+        // Half->Full with 0.5 remainder: Full should tick immediately (0.5 + 1.0 >= 1.0)
+        let mut world = bevy_ecs::world::World::new();
+        world.insert_resource(SimulationTime { tick_rate: TickRate::Half, ..Default::default() });
+        let mut schedule = bevy_ecs::schedule::Schedule::default();
+        schedule.add_systems(advance_tick);
+
+        // Frame 1: Half rate, accumulate 0.5, no tick
+        schedule.run(&mut world);
+        assert_eq!(world.resource::<SimulationTime>().tick, 0);
+
+        // Switch to Full mid-accumulation (0.5 remainder)
+        world.resource_mut::<SimulationTime>().tick_rate = TickRate::Full;
+
+        // Frame 2: Full rate adds 1.0 to 0.5 remainder → tick fires
+        schedule.run(&mut world);
+        assert_eq!(world.resource::<SimulationTime>().tick, 1);
+
+        // Switch to Paused: no advance regardless of accumulator
+        world.resource_mut::<SimulationTime>().tick_rate = TickRate::Paused;
+        schedule.run(&mut world);
+        assert_eq!(world.resource::<SimulationTime>().tick, 1);
+
+        // Switch back to Half: accumulator still has 0.5 from overshoot
+        world.resource_mut::<SimulationTime>().tick_rate = TickRate::Half;
+        schedule.run(&mut world);
+        // 0.5 (leftover) + 0.5 (Half) = 1.0 → tick fires
+        assert_eq!(world.resource::<SimulationTime>().tick, 2);
+    }
+
     #[test]
     fn half_rate_no_drift_over_10000_frames() {
         let mut world = bevy_ecs::world::World::new();