feat(animation): attach external animation files to a model

Animation-only FBX files (no mesh, clips only) could not be used:
clips are keyed by node index into the parsed model's node table, so
there was no path to get them onto a different model's skeleton.

Add AssetManager::AttachAnimationClips: parses the container with the
CPU-only path (no GPU upload -- empty meshes cannot build a Model),
remaps each clip's channels to the target model's node indices by
bone name, and appends to its clip list. Channels whose bone name is
absent are skipped and counted; clips with zero matching channels are
dropped. Same-source attach is idempotent via a new
AnimationClip::sourcePath marker; name clashes get the file stem
prefixed.

Inspector Animation block gains an attach slot (UE Details semantics)
listing model-container files plus a bullet list of attached sources;
already-attached paths are replayed idempotently when the entity is
selected, so clips survive restarts. The paths persist in the scene
(Animation.Attached); the clips themselves stay runtime state.

Limitations (documented, by design): same-skeleton retargeting only
-- bone names must match between source and target (same DCC export
or Mixamo-style per-animation downloads); cross-skeleton retargeting
is out of scope.

Engine/include/Engine/Assets/AssetManager.h

@@ -161,6 +161,20 @@ namespace Engine
             Model* GetModel(ModelRef h) const { return m_Models.Get(h); }
             void UnloadModel(ModelRef h) { m_Models.Unload(h); }
 
+            // ---- 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
+            // 重映射进目标模型的 clip 表。前提 = 源/目标骨骼命名同源（如
+            // 同一 DCC 拆分/Mixamo 同角色）；名字对不上的轨道跳过并计数。
+            // 幂等：目标 clips 已含该源（sourcePath）时不重复并入。
+            struct AnimAttachResult
+            {
+                u32 clipsAdded = 0;
+                u32 channelsMatched = 0;
+                u32 channelsSkipped = 0;   // 骨骼名在目标模型找不到
+            };
+            AnimAttachResult AttachAnimationClips(ModelRef target,
+                                                  const std::string& animPath);
+
             // 程序化平面（纯色贴图）：size 为半边长。带缓存，同参数共享一份。
             ModelRef CreatePlane(f32 halfSize, u8 r, u8 g, u8 b);
             // 半透明平面（alpha 0-255，透明绘制队列）：同参数缓存去重

Engine/include/Engine/ECS/Components.h

@@ -145,6 +145,11 @@ namespace Engine::ECS {
         f32 fadeElapsed = 0.0f;     // 已过渡时长
         f32 fadeDuration = 0.3f;    // 过渡总时长（秒）
 
+        // 外部动画资产（编辑器 attach 的动画容器文件，随场景持久化）。
+        // clips 本体运行时并入 Model 资产（共享）；重启后由 Inspector
+        // 按此列表幂等重放
+        std::vector<std::string> attachedAnimPaths;
+
         // 切换 clip（带 crossfade）。越界/空 clip 保护在消费端。
         void Play(int index, f32 fadeSeconds = 0.3f)
         {

Engine/include/Engine/Renderer/Model.h

@@ -71,6 +71,9 @@ namespace Engine
         f32 duration = 0.0f;   // 秒（已按 tps 换算）
         f32 tps = 1.0f;        // ticks per second（0 按 1，assimp 惯例）
         std::vector<AnimChannel> channels;
+        // 外部动画文件来源路径（运行时并入的 clip 标记；空 = 模型内嵌）。
+        // 用于幂等去重：同一源文件不重复并入
+        std::string sourcePath;
     };
 
     // aiNode 树拍平表：骨骼 global 变换的累乘骨架（解析期 ProcessNode
@@ -147,6 +150,15 @@ namespace Engine
         bool HasAnimations() const { return !m_Clips.empty(); }
         u32 GetBoneCount() const { return static_cast<u32>(m_Bones.size()); }
         const std::vector<AnimationClip>& GetClips() const { return m_Clips; }
+        // 外部动画并入（编辑器 attach 操作）：追加到 clip 表尾部，
+        // 既有 clipIndex 不受影响。仅运行时内存状态（重启后由场景
+        // 里 Animation.attachedAnimPaths 驱动重放）
+        void AppendClips(std::vector<AnimationClip>&& extra)
+        {
+            m_Clips.insert(m_Clips.end(),
+                           std::make_move_iterator(extra.begin()),
+                           std::make_move_iterator(extra.end()));
+        }
         const std::vector<ModelNode>& GetNodes() const { return m_Nodes; }
         const std::vector<ModelBone>& GetBones() const { return m_Bones; }