feat(03-04): FallDamageSuppressorSystem + wiring + cleanup [DBG throttle] (Task 3)

- FallDamageSuppressorSystem: subclass DamageEventSystem, cancel Damage
  cause=Fall quand guard.shouldSuppressFallDamage; FALL_INDEX lazy via
  DamageCause.getAssetMap().getIndex; groupe inspectDamageGroup
- GravityApplier: 3-arg constructor avec FallDamageGuard; first-match
  region, filtres AffectPlayers/Npcs/Items avant wake, seed addForce
  paramétré par VerticalForce (remplace hardcode 0.1); notifie
  guard.markInRegion / markExit (via lastKnownRegion map pour Pass 2)
- Cleanup: retire les AtomicInteger counters + log [DBG tick=...]
  throttle 1s; conserve logs one-shot [DBG npc.woken]/[DBG npc.ctrlNull]
- GravityFlipPlugin.setup(): instancie FallDamageGuard, registerSystem
  sur entityStoreRegistry; start() passe guard au GravityApplier
- Imports Query + CommandBuffer alignés sur FlockMembershipSystems

src/main/java/com/mythlane/gravityflip/GravityFlipPlugin.java

@@ -6,6 +6,8 @@ import com.hypixel.hytale.server.core.universe.Universe;
 import com.hypixel.hytale.server.core.universe.world.World;
 import com.hypixel.hytale.server.core.util.Config;
 import com.mythlane.gravityflip.config.GravityFlipConfig;
+import com.mythlane.gravityflip.physics.FallDamageGuard;
+import com.mythlane.gravityflip.physics.FallDamageSuppressorSystem;
 import com.mythlane.gravityflip.physics.GravityApplier;
 import com.mythlane.gravityflip.region.RegionRegistry;
 import com.mythlane.gravityflip.tick.RegionTickLoop;
@@ -38,6 +40,7 @@ public class GravityFlipPlugin extends JavaPlugin {
     private RegionRegistry registry;
     private RegionTickLoop tickLoop;
     private GravityApplier gravityApplier;
+    private FallDamageGuard fallDamageGuard;
 
     public GravityFlipPlugin(JavaPluginInit init) {
         super(init);
@@ -55,6 +58,13 @@ public class GravityFlipPlugin extends JavaPlugin {
         // a Supplier<World> that resolves Universe.get().getDefaultWorld() lazily on each
         // tick (matching the MythWorld WorldBorderManager precedent). Until the universe
         // is ready, the supplier returns null and the tick is a no-op.
+        // Plan 03-04 : enregistrer le FallDamageSuppressorSystem DANS setup() (fenêtre ECS
+        // de registration). Pattern identique à FlockPlugin.java → entityStoreRegistry.registerSystem(...).
+        this.fallDamageGuard = new FallDamageGuard();
+        getEntityStoreRegistry().registerSystem(new FallDamageSuppressorSystem(
+                fallDamageGuard,
+                th -> getLogger().at(Level.WARNING).withCause(th).log("fallDamageSuppressor handle failed")));
+
         getLogger().at(Level.INFO).log("Gravity Flip enabled");
     }
 
@@ -65,7 +75,8 @@ public class GravityFlipPlugin extends JavaPlugin {
         this.registry = new RegionRegistry(cfg, configHolder);
         this.gravityApplier = new GravityApplier(
                 th -> getLogger().at(Level.WARNING).withCause(th).log("gravityApply failed"),
-                msg -> getLogger().at(Level.INFO).log("%s", msg));
+                msg -> getLogger().at(Level.INFO).log("%s", msg),
+                fallDamageGuard);
         this.tickLoop = new RegionTickLoop(registry, gravityApplier, th ->
                 getLogger().at(Level.WARNING).withCause(th).log("detectTick failed"));