fix: stabilize block item registration and display

Store item names as owned strings in ItemManager, set block type
property for block items, validate item kind before placement, and
handle items without textures gracefully in inventory UI.

src/gameplay/item_manager.cpp

@@ -79,6 +79,7 @@ void ItemManager::add(const std::filesystem::path& path) {
         if (a->second.kind == ItemKind::BLOCK) {
             BlockType b = BlockManager::id_from_name(a->second.name);
             m_block_to_id_map.emplace(b, a->first);
+            a->second.property = b;
         }
 
     } else {
@@ -91,7 +92,7 @@ const ItemData& ItemManager::get_item_data(std::string_view key) const {
     {
         IDMap::const_accessor cacc;
 
-        if (m_id_map.find(cacc, key)) {
+        if (m_id_map.find(cacc, std::string(key))) {
             id = cacc->second;
         } else {
             Logger::error("Can't Find key {} in id map", key);