feat: add Lua 5.1 addon system with .toc loader and /run command

Foundation for WoW-compatible addon support:

- Vendor Lua 5.1.5 source as a static library (extern/lua-5.1.5)
- TocParser: parses .toc files (## directives + file lists)
- LuaEngine: Lua 5.1 VM with sandboxed stdlib (no io/os/debug),
  WoW-compatible print() that outputs to chat, GetTime() stub
- AddonManager: scans Data/interface/AddOns/ for .toc files,
  loads .lua files on world entry, skips LoadOnDemand addons
- /run <code> slash command for inline Lua execution
- HelloWorld test addon that prints to chat on load

Integration: AddonManager initialized after asset manager, addons
loaded once on first world entry, reset on logout. XML frame
parsing is deferred to a future step.

src/core/application.cpp

@@ -31,6 +31,7 @@
 #include "audio/footstep_manager.hpp"
 #include "audio/activity_sound_manager.hpp"
 #include "audio/audio_engine.hpp"
+#include "addons/addon_manager.hpp"
 #include <imgui.h>
 #include "pipeline/m2_loader.hpp"
 #include "pipeline/wmo_loader.hpp"
@@ -329,6 +330,17 @@ bool Application::initialize() {
             }
         }
 
+        // Initialize addon system
+        addonManager_ = std::make_unique<addons::AddonManager>();
+        if (addonManager_->initialize(gameHandler.get())) {
+            std::string addonsDir = assetPath + "/interface/AddOns";
+            addonManager_->scanAddons(addonsDir);
+            LOG_INFO("Addon system initialized, found ", addonManager_->getAddons().size(), " addon(s)");
+        } else {
+            LOG_WARNING("Failed to initialize addon system");
+            addonManager_.reset();
+        }
+
     } else {
         LOG_WARNING("Failed to initialize asset manager - asset loading will be unavailable");
         LOG_WARNING("Set WOW_DATA_PATH environment variable to your WoW Data directory");
@@ -650,6 +662,7 @@ void Application::setState(AppState newState) {
             // If we reuse a previously spawned instance without forcing a respawn, appearance (notably hair) can desync.
             npcsSpawned = false;
             playerCharacterSpawned = false;
+            addonsLoaded_ = false;
             weaponsSheathed_ = false;
             wasAutoAttacking_ = false;
             loadedMapId_ = 0xFFFFFFFF;
@@ -5031,6 +5044,12 @@ void Application::loadOnlineWorldTerrain(uint32_t mapId, float x, float y, float
 
     // Only enter IN_GAME when this is the final map (no deferred entry pending).
     setState(AppState::IN_GAME);
+
+    // Load addons once per session on first world entry
+    if (addonManager_ && !addonsLoaded_) {
+        addonManager_->loadAllAddons();
+        addonsLoaded_ = true;
+    }
 }
 
 void Application::buildCharSectionsCache() {