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/include/Engine/Assets/AssetManager.h

@@ -117,6 +117,17 @@ namespace Engine
                 return (e.generation == h.generation && e.alive) ? e.path : kEmpty;
             }
 
+            // 按路径查活资产（未加载/已卸载返回 nullptr；不触发加载、
+            // 不对坏句柄 FATAL）——面板展示用
+            T* Find(const std::string& path) const
+            {
+                auto it = m_ByPath.find(path);
+                if (it == m_ByPath.end()) return nullptr;
+                const Entry& e = m_Entries[it->second.index];
+                return (e.alive && e.generation == it->second.generation)
+                           ? e.asset.get() : nullptr;
+            }
+
             u32 Count() const
             {
                 return static_cast<u32>(m_Entries.size()) - static_cast<u32>(m_Free.size());
@@ -160,6 +171,12 @@ namespace Engine
             ModelRef LoadModel(const std::string& path, ParsedModel&& parsed);
             Model* GetModel(ModelRef h) const { return m_Models.Get(h); }
             void UnloadModel(ModelRef h) { m_Models.Unload(h); }
+            // 按路径查已加载的模型（未加载返回 null，不触发加载）——
+            // 面板 hover 信息卡用
+            Model* GetModelByPath(const std::string& path) const
+            {
+                return m_Models.Find(path);
+            }
 
             // ---- 外部动画并入（UE AnimSequence 归属 Skeleton 的简化版）----
             // 把动画容器文件（无网格 FBX/GLB 等）里的 clip 按骨骼节点名

Engine/include/Engine/Renderer/Model.h

@@ -99,7 +99,10 @@ namespace Engine
         std::vector<ModelNode> nodes;
         std::vector<ModelBone> bones;
         std::vector<AnimationClip> clips;
-        bool Valid() const { return !meshes.empty(); }
+        // 解析有效性：mesh 与 clip 至少其一非空。纯动画 FBX（无网格只有
+        // 骨骼动画，UE 的 Animation Sequence 资产同理）是合法资产——
+        // 过去只认 meshes 导致动画源文件在缓存层被整体拒载
+        bool Valid() const { return !meshes.empty() || !clips.empty(); }
     };
 
     class Model