fix: animation-only FBX assets loadable; clip data viewer

Pure-animation FBX (no meshes, skeleton clips only) was rejected at
the cache layer: ParsedModel::Valid() required non-empty meshes, so
Model::FromParsed/LoadModel returned null and the asset never made it
into the cache. Animation assets are now first-class:

- ParsedModel::Valid() = meshes or clips non-empty; parse failures
  (both empty) still rejected. Empty-mesh consumers already guarded
  (rendering skips empty mesh loop, mesh collider falls back to Box)
- ParseFromDisk: fix null-deref when assimp returns a null scene
- AssetCache::Find(path) + AssetManager::GetModelByPath for panels
- Asset Browser hover card shows meshes/bones/clips for loaded models
- Inspector model line flags "animation-only" when meshes == 0
- Animation section: collapsible clip data table (name/duration/
  channel count) to verify bone-name matching of attached clips

App/editor/AssetBrowserPanel.cpp

@@ -342,6 +342,20 @@ void AssetBrowserPanel::DrawFileList(const EditorContext& ctx,
                     state = "loaded";
                 }
                 ImGui::Text("state: %s", state);
+                // 已加载的 model 展开资产数据概览（meshes=0 即纯动画
+                // 容器；未加载不显示——查询不触发加载）
+                if (item.kind == Kind::Model)
+                {
+                    if (const Engine::Model* m =
+                            ctx.assets->GetModelByPath(assetPath);
+                        m != nullptr)
+                    {
+                        ImGui::Text("meshes: %u, bones: %u, clips: %u",
+                                    static_cast<unsigned>(m->GetMeshes().size()),
+                                    m->GetBoneCount(),
+                                    static_cast<unsigned>(m->GetClips().size()));
+                    }
+                }
             }
             ImGui::TextDisabled("%s", assetPath.c_str());
             ImGui::EndTooltip();