Replace flat mesh rendering of additive/mod blend batches (blendMode >= 3)
with camera-facing point sprites using a soft radial gradient texture and
additive blending. Adds M2 particle emitter infrastructure (structs, shader,
parsing stubs) but disables emitter parsing — the assumed 476-byte struct
size is wrong for WotLK 3.3.5a, causing misaligned reads that explode RAM.