Batches whose named texture fails to load now render invisible instead of
white (the swampreeds01a.blp case causing a white shell around aquatic plants).
Also implements proper M2 opacity plumbing:
- Parse texture weight tracks (M2Track<fixed16>) and color animation alpha
tracks (M2Color.alpha) to resolve per-batch opacity at load time
- Skip batches with batchOpacity < 0.01 in the render loop
- Apply M2Texture.flags (bit0=WrapS, bit1=WrapT) to GL sampler wrap mode
- Upload both UV sets (texCoords[0] and texCoords[1]) and select via
textureUnit uniform, so batches referencing UV set 1 render correctly
794ad9aee4