Add animation controller system, material assets and skeleton visualization

- .animctrl state machine asset (params/transitions/blend trees, 1D+2D
  directional blending) with Unity Animator-style editor panel: state
  list, transitions, params, directional pad preview driving live
  CrossFade on the selected entity
- Split animation evaluation out of SceneRenderer into
  AnimationSystem/AnimationEvaluator; skin palettes with rest-pose
  fallback and blend-weight epsilon filtering
- MaterialAsset (.material) with reload-safe preview tile pool
  (DropMaterial clears dirty refs before instance destruction)
- EditorGizmoPass skeleton wires + viewport joint overlay; camera
  projection rework (baked Vulkan Y-flip, ortho support)
- Editor/game build split via HELLOVULKAN_EDITOR option

shaders/gizmo_billboard.vert

@@ -0,0 +1,22 @@
+#version 450
+
+// Editor gizmo billboard 顶点：世界空间 billboard quad（CPU 侧已面向相机
+// 展开），无描述符 set——viewProj 走 push constant（与 debug_line 同约定）。
+// aux = (shapeId, uv.x, uv.y, 0)，uv ∈ [-1,1] 供片元 SDF 造型。
+
+layout(location = 0) in vec3 inPos;
+layout(location = 1) in vec4 inColor;
+layout(location = 2) in vec4 inAux;
+
+layout(location = 0) out vec4 outColor;
+layout(location = 1) out vec4 outAux;
+
+layout(push_constant) uniform PC {
+    mat4 viewProj;
+} pc;
+
+void main() {
+    gl_Position = pc.viewProj * vec4(inPos, 1.0);
+    outColor = inColor;
+    outAux = inAux;
+}