Three new scene shaders to widen the library, now that the main families are
settled. Each is a shader plus a params block, registered in the single
source of truth (scenes/registry.js), so casting, UI, arc and checks pick
them up automatically.
- Block Mosh (glitch): a datamosh. Blocks pull the feedback buffer along
per-block strokes on a bar-quantized grid so the corruption steps like an
edit rather than crawling, and spills on onsets. Fills the most iconic
gap in the glitch family.
- Neon City (structural): a receding skyline with instanced lit windows,
distinct from the rolling ridgelines and the road grid it sits alongside.
- Flora (organic): an abstract plant of swaying stalks, teardrop petals and
a bloom corona, all stamped in the track's signature shape.
Also adds HOWTO-visualizers.md, a quick reference for building the next one.
