feat: display Lua addon errors as in-game UI errors

Previously Lua addon errors only logged to the log file. Now they
display as red UI error text to the player (same as spell errors and
game warnings), helping addon developers debug issues in real-time.

Add LuaErrorCallback to LuaEngine, fire it from event handler and
frame OnEvent pcall error paths. Wire the callback to GameHandler's
addUIError in application.cpp.

include/addons/lua_engine.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <functional>
 #include <string>
 #include <vector>
 
@@ -47,9 +48,14 @@ public:
     lua_State* getState() { return L_; }
     bool isInitialized() const { return L_ != nullptr; }
 
+    // Optional callback for Lua errors (displayed as UI errors to the player)
+    using LuaErrorCallback = std::function<void(const std::string&)>;
+    void setLuaErrorCallback(LuaErrorCallback cb) { luaErrorCallback_ = std::move(cb); }
+
 private:
     lua_State* L_ = nullptr;
     game::GameHandler* gameHandler_ = nullptr;
+    LuaErrorCallback luaErrorCallback_;
 
     void registerCoreAPI();
     void registerEventAPI();

src/addons/lua_engine.cpp

@@ -3820,8 +3820,9 @@ void LuaEngine::fireEvent(const std::string& eventName,
         int nargs = 1 + static_cast<int>(args.size());
         if (lua_pcall(L_, nargs, 0, 0) != 0) {
             const char* err = lua_tostring(L_, -1);
-            LOG_ERROR("LuaEngine: event '", eventName, "' handler error: ",
+            std::string errStr = err ? err : "(unknown)";
-                      err ? err : "(unknown)");
+            LOG_ERROR("LuaEngine: event '", eventName, "' handler error: ", errStr);
+            if (luaErrorCallback_) luaErrorCallback_(errStr);
             lua_pop(L_, 1);
         }
     }
@@ -3847,7 +3848,10 @@ void LuaEngine::fireEvent(const std::string& eventName,
                         for (const auto& arg : args) lua_pushstring(L_, arg.c_str());
                         int nargs = 2 + static_cast<int>(args.size());
                         if (lua_pcall(L_, nargs, 0, 0) != 0) {
-                            LOG_ERROR("LuaEngine: frame OnEvent error: ", lua_tostring(L_, -1));
+                            const char* ferr = lua_tostring(L_, -1);
+                            std::string ferrStr = ferr ? ferr : "(unknown)";
+                            LOG_ERROR("LuaEngine: frame OnEvent error: ", ferrStr);
+                            if (luaErrorCallback_) luaErrorCallback_(ferrStr);
                             lua_pop(L_, 1);
                         }
                     } else {

src/core/application.cpp

@@ -335,6 +335,10 @@ bool Application::initialize() {
         if (addonManager_->initialize(gameHandler.get())) {
             std::string addonsDir = assetPath + "/interface/AddOns";
             addonManager_->scanAddons(addonsDir);
+            // Wire Lua errors to UI error display
+            addonManager_->getLuaEngine()->setLuaErrorCallback([gh = gameHandler.get()](const std::string& err) {
+                if (gh) gh->addUIError(err);
+            });
             // Wire chat messages to addon event dispatch
             gameHandler->setAddonChatCallback([this](const game::MessageChatData& msg) {
                 if (!addonManager_ || !addonsLoaded_) return;