feat(04-02): register /gravityflip command in start() (CMD-01)

- wire getCommandRegistry().registerCommand(new GravityFlipCommand(this))
- import com.mythlane.gravityflip.command.GravityFlipCommand
- no manual cleanup: CommandRegistry.register auto-adds shutdownTask

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

@@ -14,6 +14,7 @@ import com.mythlane.gravityflip.physics.GravityApplier;
 import com.mythlane.gravityflip.region.GravityFlipRegion;
 import com.mythlane.gravityflip.region.RegionRegistry;
 import com.mythlane.gravityflip.tick.RegionTickLoop;
+import com.mythlane.gravityflip.command.GravityFlipCommand;
 import com.mythlane.gravityflip.viz.RegionVisualizer;
 import com.mythlane.gravityflip.wand.GravityFlipWandInteraction;
 import com.mythlane.gravityflip.wand.WandSelectionStore;
@@ -122,6 +123,11 @@ public class GravityFlipPlugin extends JavaPlugin {
             getTaskRegistry().registerTask(vf);
         } catch (Throwable ignored) { /* manual shutdown() fallback */ }
 
+        // Plan 04-02 : enregistrer la commande racine /gravityflip + sous-commande `wand`.
+        // Pattern : CommandRegistry.register(...) ajoute automatiquement un shutdownTask qui
+        // unregister au teardown (cf. CommandRegistry base class). Pas de cleanup manuel.
+        getCommandRegistry().registerCommand(new GravityFlipCommand(this));
+
         getLogger().at(Level.INFO).log(
                 "Gravity Flip enabled — %d region(s) loaded, detector @100ms, gravity inversion active",
                 cfg.getRegions().size());