vfx-review (effects review loop)

Why it exists: an effect once went through eight rejected rounds ("stickers", "laggy and choppy", "looks flat", then "just get rid of it") while self-reviews kept approving. The reviewer saw stills where particles weren't simulating, knew the intent, and compared with the last round instead of the goal. Each step below fixes one of those. Roblox facts: references/roblox_vfx_facts.md; what was tried before: vault/Pipelines/VFX and Particles.md; look rules: vault/Style Bible.md §5; where to find textures and packs: vault/Pipelines/Asset Library.md.