feat(03-01): wire GravityApplier into RegionTickLoop + plugin (Task 2)

- RegionTickLoop gagne un constructeur 3-args (registry, gravityApplier, errorHandler)
- Ancien constructeur 2-args conservé pour rétrocompat des tests Phase 02
- Tick body appelle gravityApplier.apply(w, registry.currentSnapshot(w)) après refreshFor
- GravityFlipPlugin.start() construit l'applier et l'injecte dans le tickLoop
- Log de démarrage mis à jour: 'gravity inversion active'

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

@@ -6,6 +6,7 @@ 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.GravityApplier;
 import com.mythlane.gravityflip.region.RegionRegistry;
 import com.mythlane.gravityflip.tick.RegionTickLoop;
 
@@ -36,6 +37,7 @@ public class GravityFlipPlugin extends JavaPlugin {
 
     private RegionRegistry registry;
     private RegionTickLoop tickLoop;
+    private GravityApplier gravityApplier;
 
     public GravityFlipPlugin(JavaPluginInit init) {
         super(init);
@@ -61,7 +63,9 @@ public class GravityFlipPlugin extends JavaPlugin {
         super.start();
         GravityFlipConfig cfg = configHolder.get();
         this.registry = new RegionRegistry(cfg, configHolder);
-        this.tickLoop = new RegionTickLoop(registry, th ->
+        this.gravityApplier = new GravityApplier(th ->
+                getLogger().at(Level.WARNING).withCause(th).log("gravityApply failed"));
+        this.tickLoop = new RegionTickLoop(registry, gravityApplier, th ->
                 getLogger().at(Level.WARNING).withCause(th).log("detectTick failed"));
 
         // Lazy world resolution — see setup() comment.
@@ -81,7 +85,7 @@ public class GravityFlipPlugin extends JavaPlugin {
         } catch (Throwable ignored) { /* manual shutdown() fallback */ }
 
         getLogger().at(Level.INFO).log(
-                "Gravity Flip enabled — %d region(s) loaded, detector @100ms",
+                "Gravity Flip enabled — %d region(s) loaded, detector @100ms, gravity inversion active",
                 cfg.getRegions().size());
     }