fix(simulation): address PR #2 review findings

- Fix Cargo.toml edition 2024 → 2021 (Hoshe #1)
- Switch test runner to cargo-nextest in Makefile (Hoshe #2, D-030)
- Add debug_assert tick ordering enforcement in InputQueue::push (Hoshe #4)
- Add DayPhase Serialize/Deserialize derives (Tyre #6)
- Add day phase boundary comments clarifying half-open ranges (Hoshe #3)
- Add phase duration adjustability comment (Tyre #5)
- Document ObserverSnapshot planned fields as TODO (Tyre #1)
- Document entity_id as wire-format ID, not ECS Entity (Tyre #2)
- Change Relationship.target_name to target_id: u64 (Tyre #3)
- Clarify single app.update() is intentional boilerplate (Hoshe #8, Tyre #7)

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

server/src/simulation/time.rs

@@ -3,12 +3,14 @@
 // Injectable time resource for deterministic replay (D-030)
 
 use bevy_ecs::prelude::*;
+use serde::{Deserialize, Serialize};
 
 pub const TICKS_PER_GAME_MINUTE: u64 = 10;
 pub const MINUTES_PER_PHASE: u64 = 360;
 pub const MINUTES_PER_DAY: u64 = 1440;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+// 4 equal 6-hour phases (adjustable — D-031 allows rebalancing phase durations)
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub enum DayPhase {
     Morning,
     Afternoon,
@@ -33,6 +35,7 @@ impl SimulationTime {
     }
     pub fn day_phase(&self) -> DayPhase {
         let tod = self.time_of_day_minutes();
+        // Morning: [0, 360), Afternoon: [360, 720), Evening: [720, 1080), Night: [1080, 1440)
         match tod {
             0..360 => DayPhase::Morning,
             360..720 => DayPhase::Afternoon,
@@ -114,4 +117,25 @@ mod tests {
         schedule.run(&mut world);
         assert_eq!(world.resource::<SimulationTime>().tick, 1);
     }
+
+    #[test]
+    fn day_wraparound_at_midnight() {
+        // 1440 minutes = 1 full day, should wrap back to Morning
+        let time = SimulationTime {
+            tick: MINUTES_PER_DAY * TICKS_PER_GAME_MINUTE,
+            paused: false,
+        };
+        assert_eq!(time.day_phase(), DayPhase::Morning);
+        assert_eq!(time.time_of_day_minutes(), 0);
+        assert_eq!(time.day(), 1);
+    }
+
+    #[test]
+    fn day_calculation() {
+        let time = SimulationTime {
+            tick: 3 * MINUTES_PER_DAY * TICKS_PER_GAME_MINUTE + 100,
+            paused: false,
+        };
+        assert_eq!(time.day(), 3);
+    }
 }