fix(editor): unload ghost preview model when path changes

setGhostPreview reused modelId 59999 for every preview, but loadModel
returns true without doing anything when the ID is already cached. So
selecting a new NPC kept the old ghost model in GPU memory and createInstance
used the stale model. Added M2Renderer::unloadModel public API and call it
from clearGhostPreview.

include/rendering/m2_renderer.hpp

@@ -287,6 +287,8 @@ public:
 
     bool hasModel(uint32_t modelId) const;
     bool loadModel(const pipeline::M2Model& model, uint32_t modelId);
+    /** Force-remove a model and all its GPU resources. Caller must ensure no instances reference it. */
+    void unloadModel(uint32_t modelId);
     /** Mark a loaded model as a spell effect (full-brightness particles, no collision). */
     void markModelAsSpellEffect(uint32_t modelId);
 

src/rendering/m2_renderer_instance.cpp

@@ -543,6 +543,15 @@ void M2Renderer::cleanupUnusedModels() {
     }
 }
 
+void M2Renderer::unloadModel(uint32_t modelId) {
+    auto it = models.find(modelId);
+    if (it == models.end()) return;
+    if (vkCtx_) vkDeviceWaitIdle(vkCtx_->getDevice());
+    destroyModelGPU(it->second);
+    models.erase(it);
+    modelUnusedSince_.erase(modelId);
+}
+
 VkTexture* M2Renderer::loadTexture(const std::string& path, uint32_t texFlags) {
     constexpr uint64_t kFailedTextureRetryLookups = 512;
     auto normalizeKey = [](std::string key) {

tools/editor/editor_viewport.cpp

@@ -623,7 +623,9 @@ void EditorViewport::clearGhostPreview() {
         ghostInstanceId_ = 0;
     }
     if (ghostModelId_ != 0 && m2Renderer_) {
-        // Don't unload the model — it might be used by placed objects too
+        // Ghost ID is reserved for previews only — safe to unload so a path
+        // change can re-load with the new model under the same ID.
+        m2Renderer_->unloadModel(ghostModelId_);
         ghostModelId_ = 0;
         ghostModelPath_.clear();
     }