fix(04-bugfix): move wand JSON to Server/Item/Items/ and clone Weapon_Wand_Root template

Empirical findings from HytaleServer.jar decompile + Assets.zip introspection:
- AssetRegistryLoader.loadAssets0() resolves each plugin asset-pack root to
  <root>/Server/, then iterates AssetStores and loads from
  Server/<assetStore.getPath()>/. For the Item AssetStore, path is
  'Item/Items'. So the wand JSON MUST live at Server/Item/Items/.
- The previous src/main/resources/Items/gravityflip_wand.json path was
  never scanned: the loader would look at <jar>/Server/Item/Items/.
- Key function is Item::getId with item.id = blockTypeKey (filename minus
  .json). So file 'gravityflip_wand.json' -> lookup id 'gravityflip_wand'.

JSON content cloned from vanilla Weapon_Wand_Root.json (extracted from
HYTALE SERVER/Assets.zip), which is the minimal wand template:
- Categories: ['Items.Weapons'] -> shows up in builder/creative menu.
- Icon/Model/Texture reuse vanilla wand assets (no custom art shipped).
- PlayerAnimationsId: Wand -> proper holding animation.
- ItemSoundSetId: ISS_Weapons_Wand -> pickup/drop SFX.
- Utility.Compatible=true and Weapon={} keep it functional in builder tools.
- Interactions.Primary/Secondary are inline {Type: GravityFlipWand} objects,
  which the plugin's CodecRegistry(Interaction.CODEC).register call binds
  to GravityFlipWandInteraction.CODEC (04-01 pattern, Finding 3).

src/main/resources/Items/gravityflip_wand.json

@@ -1,16 +0,0 @@
-{
-  "Icon": "Torch_Fire",
-  "TranslationProperties": {
-    "Translation": "Gravity Flip Wand"
-  },
-  "ResourceType": "Utility",
-  "MaxStackSize": 1,
-  "Interactions": {
-    "Primary": {
-      "Type": "GravityFlipWand"
-    },
-    "Secondary": {
-      "Type": "GravityFlipWand"
-    }
-  }
-}

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

@@ -0,0 +1,50 @@
+{
+  "TranslationProperties": {
+    "Name": "Gravity Flip Wand",
+    "Description": "Primary click: set pos1. Secondary click: set pos2. Use /gravityflip define to finalise a region."
+  },
+  "Categories": [
+    "Items.Weapons"
+  ],
+  "Icon": "Icons/ItemsGenerated/Weapon_Wand_Wood.png",
+  "Quality": "Rare",
+  "ItemLevel": 40,
+  "Model": "Items/Weapons/Wand/Wood.blockymodel",
+  "Texture": "Items/Weapons/Wand/Wood_Texture.png",
+  "PlayerAnimationsId": "Wand",
+  "Utility": {
+    "Compatible": true
+  },
+  "Interactions": {
+    "Primary": {
+      "Type": "GravityFlipWand"
+    },
+    "Secondary": {
+      "Type": "GravityFlipWand"
+    }
+  },
+  "IconProperties": {
+    "Scale": 0.6,
+    "Translation": [
+      -13,
+      -16
+    ],
+    "Rotation": [
+      45,
+      90,
+      0
+    ]
+  },
+  "DroppedItemAnimation": "Items/Animations/Dropped/Dropped_Diagonal_Left.blockyanim",
+  "Tags": {
+    "Type": [
+      "Weapon"
+    ],
+    "Family": [
+      "Wand"
+    ]
+  },
+  "Weapon": {},
+  "ItemSoundSetId": "ISS_Weapons_Wand",
+  "MaxStackSize": 1
+}