refactor(item): decouple items from block types

The item system now supports an ItemKind and property, allowing item JSON to declare a type instead of assuming every item is a block. BlockManager was moved to its own header, redesigned around concurrent hash maps, and exposes id_from_name(). Texture and UI code now key items by ItemID, while block placement resolves the block type from the item registry.

assets/item/air.json

@@ -1,5 +1,6 @@
 {
     "id": 0,
     "name": "air",
-    "description": ""
+    "description": "",
+    "type": "block"
 }

assets/item/dirt.json

@@ -2,5 +2,6 @@
     "id": 2,
     "name": "dirt",
     "description": "",
-    "texture": "texture/item/block/dirt.png"
-}
+    "texture": "texture/item/block/dirt.png",
+    "type": "block"
+}

assets/item/grass.json

@@ -2,5 +2,6 @@
     "id": 9,
     "name": "grass",
     "description": "",
-    "texture": "texture/item/block/grass.png"
-}
+    "texture": "texture/item/block/grass.png",
+    "type": "block"
+}

assets/item/grass_block.json

@@ -2,5 +2,6 @@
     "id": 1,
     "name": "grass_block",
     "description": "",
-    "texture": "texture/item/block/grass_block.png"
+    "texture": "texture/item/block/grass_block.png",
+    "type": "block"
 }

assets/item/leaf.json

@@ -2,5 +2,6 @@
     "id": 6,
     "name": "leaf",
     "description": "",
-    "texture": "texture/item/block/leaf.png"
-}
+    "texture": "texture/item/block/leaf.png",
+    "type": "block"
+}

assets/item/log.json

@@ -2,5 +2,6 @@
     "id": 5,
     "name": "log",
     "description": "",
-    "texture": "texture/item/block/log.png"
-}
+    "texture": "texture/item/block/log.png",
+    "type": "block"
+}

assets/item/sand.json

@@ -2,5 +2,6 @@
     "id": 4,
     "name": "sand",
     "description": "",
-    "texture": "texture/item/block/sand.png"
-}
+    "texture": "texture/item/block/sand.png",
+    "type": "block"
+}

assets/item/snowy_grass_block.json

@@ -2,5 +2,6 @@
     "id": 8,
     "name": "snowy_grass_block",
     "description": "",
-    "texture": "texture/item/block/snowy_grass_block.png"
-}
+    "texture": "texture/item/block/snowy_grass_block.png",
+    "type": "block"
+}

assets/item/stone.json

@@ -2,5 +2,6 @@
     "id": 3,
     "name": "stone",
     "description": "",
-    "texture": "texture/item/block/stone.png"
-}
+    "texture": "texture/item/block/stone.png",
+    "type": "block"
+}

assets/item/water.json

@@ -2,5 +2,6 @@
     "id": 7,
     "name": "water",
     "description": "",
-    "texture": "texture/item/block/water.png"
-}
+    "texture": "texture/item/block/water.png",
+    "type": "block"
+}