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

Engine/src/Renderer/Model.cpp

@@ -194,7 +194,8 @@ ParsedModel Model::ParseFromDisk(const std::string& path)
         aiProcess_LimitBoneWeights);   // 每顶点限 4 权重（= 顶点格式 boneIds 容量）
 
     if (!scene || (scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE) || !scene->mRootNode) {
-        if (!scene->mNumMeshes) {
+        // scene 可能为 null（文件损坏/格式不支持），先判空再打印资产清单
+        if (scene != nullptr) {
             ENGINE_WARN("Assimp warn: model dose not have mesh assets\nmodel has following asset:");
 
             ENGINE_WARN("\tMeshes Count: {}", scene->mNumMeshes);
@@ -204,10 +205,9 @@ ParsedModel Model::ParseFromDisk(const std::string& path)
             ENGINE_WARN("\tMaterials Count: {}", scene->mNumMaterials);
             ENGINE_WARN("\tSkeletons Count: {}", scene->mNumSkeletons);
             ENGINE_WARN("\tTextures Count: {}", scene->mNumTextures);
-
         }
         ENGINE_ERROR("Assimp error: {}", importer.GetErrorString());
-        return out;   // meshes 空 = 无效
+        return out;   // meshes/clips 空 = 无效
     }
 
     // 骨骼动画三件套：node 表（global 累乘骨架）→ 动画轨道 → 骨骼注册