fix(04-bugfix): wire wand via RootInteraction asset (NPE on click)

Root cause: Item.Interactions map value codec is RootInteraction.CHILD_ASSET_CODEC
(expects a String asset id referencing an asset under Item/RootInteractions/), not
an inline Interaction object. Previous JSON used "Primary": { "Type": "GravityFlipWand" }
which silently loaded a RootInteraction asset with no interactionIds -> operations[]
empty -> InteractionManager.serverTick NPE on operation.getWaitForDataFrom() when
the click chain ticked.

Fix:
- New Interaction asset Server/Item/Interactions/gravityflip_wand_click.json
  ({"Type": "GravityFlipWand"}) matching our registered Interaction subtype.
- New RootInteraction asset Server/Item/RootInteractions/gravityflip_wand_root.json
  wrapping the interaction id in its Interactions[] list (required by RootInteraction
  CODEC, see RootInteraction.build() -> OperationsBuilder).
- Item JSON now references the RootInteraction by id:
  "Interactions": { "Primary": "gravityflip_wand_root", "Secondary": "gravityflip_wand_root" }
  matching vanilla Weapon_Wand_Wood.json pattern ("Primary": "Wand_Primary").

Binding (Interaction.CODEC.register("GravityFlipWand", ...)) is unchanged and
correct -- subtype registration on the Interaction AssetCodecMapCodec, consistent
with InstancesPlugin/ExitInstanceInteraction pattern.

src/main/resources/Server/Item/Interactions/gravityflip_wand_click.json

@@ -0,0 +1,3 @@
+{
+  "Type": "GravityFlipWand"
+}

src/main/resources/Server/Item/Items/gravityflip_wand.json

@@ -16,12 +16,8 @@
     "Compatible": true
   },
   "Interactions": {
-    "Primary": {
-      "Type": "GravityFlipWand"
-    },
-    "Secondary": {
-      "Type": "GravityFlipWand"
-    }
+    "Primary": "gravityflip_wand_root",
+    "Secondary": "gravityflip_wand_root"
   },
   "IconProperties": {
     "Scale": 0.6,

src/main/resources/Server/Item/RootInteractions/gravityflip_wand_root.json

@@ -0,0 +1,5 @@
+{
+  "Interactions": [
+    "gravityflip_wand_click"
+  ]
+}