Vanilla/Turtle WoW support: M2 loading, bone parsing, textures, auth

- Vanilla M2 bone struct (108 bytes) with 28-byte animation tracks
- Version-aware bone parsing (vanilla vs WotLK format detection)
- Fix CharSections.dbc field layout for vanilla (variation/color at 4-5)
- Remove broken CharSections.csv files (all fields marked as strings)
- Expansion data reload on profile switch (DBC cache clear, layout reload)
- Vanilla packet encryption (VanillaCrypt XOR-based header crypt)
- Extended character preview geoset range (0-99) for vanilla models
- DBC cache clear support in AssetManager

src/game/update_field_table.cpp

@@ -95,6 +95,7 @@ bool UpdateFieldTable::loadFromJson(const std::string& path) {
 
     std::string json((std::istreambuf_iterator<char>(f)), std::istreambuf_iterator<char>());
 
+    auto savedFieldMap = fieldMap_;
     fieldMap_.clear();
     size_t loaded = 0;
     size_t pos = 0;
@@ -139,8 +140,14 @@ bool UpdateFieldTable::loadFromJson(const std::string& path) {
         pos = valEnd + 1;
     }
 
+    if (loaded == 0) {
+        LOG_WARNING("UpdateFieldTable: no fields loaded from ", path, ", restoring previous table");
+        fieldMap_ = std::move(savedFieldMap);
+        return false;
+    }
+
     LOG_INFO("UpdateFieldTable: loaded ", loaded, " fields from ", path);
-    return loaded > 0;
+    return true;
 }
 
 uint16_t UpdateFieldTable::index(UF field) const {