fix(simulation): correct CONTAMINATION_DELAY_TICKS from 1800 to 300

The constant was supposed to represent 30 game-minutes but the formula
was wrong (30 × 10 tps × 60s = 1800). Correct derivation: 30 minutes ×
TICKS_PER_GAME_MINUTE (10) = 300. Now uses the canonical constant
directly. Also fixes stale assertion message in integration test.

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

server/tests/contamination.rs

@@ -42,10 +42,10 @@ fn make_triangle(
     }
 }
 
-/// Acceptance test: run 1801 ticks, assert ContaminationActive is set and
-/// all ActiveFork TriangleState entities have tension > 0.
+/// Acceptance test: run past CONTAMINATION_DELAY_TICKS, assert ContaminationActive
+/// is set and all ActiveFork TriangleState entities have tension > 0.
 #[test]
-fn contamination_activates_after_1801_ticks() {
+fn contamination_activates_after_delay() {
     let mut world = World::new();
     world.init_resource::<SimulationTime>();
     world.init_resource::<ContaminationActive>();
@@ -102,8 +102,8 @@ fn contamination_activates_after_1801_ticks() {
     let mut schedule = Schedule::default();
     schedule.add_systems(tick_contamination_activation);
 
-    // Simulate 1801 ticks
-    for tick in 0..=1800 {
+    // Simulate past the delay threshold (CONTAMINATION_DELAY_TICKS = 300)
+    for tick in 0..=CONTAMINATION_DELAY_TICKS {
         world.resource_mut::<SimulationTime>().tick = tick;
         schedule.run(&mut world);
     }
@@ -111,7 +111,8 @@ fn contamination_activates_after_1801_ticks() {
     // Assert ContaminationActive is set
     assert!(
         world.resource::<ContaminationActive>().0,
-        "ContaminationActive must be true after 1801 ticks"
+        "ContaminationActive must be true after CONTAMINATION_DELAY_TICKS ({}) ticks",
+            CONTAMINATION_DELAY_TICKS
     );
 
     // Assert all ActiveFork triangles have tension > 0