feat(wom): add WOM3 multi-batch format for material-aware models

WOM1/WOM2 had a single mesh with one texture, which lost the multi-submesh
structure of complex M2 models (body+hair+eyes+armor each need different
textures and blend modes).

WOM3 adds a Batch array: each batch has indexStart/indexCount + a textureIndex
into texturePaths + blendMode + flags. Loader is fully backward compatible:
WOM1/WOM2 files still load, and WOM3 with no batches block falls back to a
single full-mesh batch. fromM2 now extracts batches with materials, and toM2
emits matching M2 batches so the renderer can draw them correctly.

include/pipeline/wowee_model.hpp

@@ -12,7 +12,7 @@ namespace pipeline {
 struct M2Model;
 
 // Wowee Open Model format (.wom) — novel format, no Blizzard IP
-// WOM1: static geometry | WOM2: + bones + animations
+// WOM1: static geometry | WOM2: + bones + animations | WOM3: + multi-batch materials
 struct WoweeModel {
     struct Vertex {
         glm::vec3 position;
@@ -43,18 +43,31 @@ struct WoweeModel {
         std::vector<std::vector<AnimKeyframe>> boneKeyframes; // [boneIdx][keyframe]
     };
 
+    // WOM3: a contiguous slice of indices that draws with one material/texture.
+    // Most M2 models have multiple submeshes (body, hair, eyes, etc.) — each
+    // becomes one Batch in WOM3.
+    struct Batch {
+        uint32_t indexStart = 0;       // first index in the global index buffer
+        uint32_t indexCount = 0;       // number of indices to draw
+        uint32_t textureIndex = 0;     // index into texturePaths
+        uint16_t blendMode = 0;        // 0=opaque, 1=alpha-test, 2=alpha, 3=add
+        uint16_t flags = 0;            // bit 0 = unlit, bit 1 = two-sided, bit 2 = no z-write
+    };
+
     std::string name;
     std::vector<Vertex> vertices;
     std::vector<uint32_t> indices;
     std::vector<std::string> texturePaths;
     std::vector<Bone> bones;
     std::vector<Animation> animations;
+    std::vector<Batch> batches;        // empty in WOM1/WOM2, populated in WOM3
     float boundRadius = 1.0f;
     glm::vec3 boundMin{0}, boundMax{0};
-    uint32_t version = 1; // 1=WOM1(static), 2=WOM2(animated)
+    uint32_t version = 1; // 1=WOM1(static), 2=WOM2(animated), 3=WOM3(multi-batch)
 
     bool isValid() const { return !vertices.empty() && !indices.empty(); }
     bool hasAnimation() const { return !bones.empty() && !animations.empty(); }
+    bool hasBatches() const { return !batches.empty(); }
 };
 
 class WoweeModelLoader {