Add point-cloud-driven fluid visuals

[Lyptik]

Summary

Adds a GPU fluid layer inspired by Pavel Dobryakov's WebGL Fluid Simulation while keeping the current WebDemo / Three.js base intact.

Behavior

• current point-cloud samples continuously seed the fluid dye field
• cluster velocity pushes the fluid in the tracked motion direction
• local point offsets add a subtle swirl around the body/object shape
• the original point cloud is drawn on top, so the tracked silhouette stays readable
• fluid is composited with a screen blend behind points/bounds/labels
• fluid naturally dissipates when tracking disappears
• WebGL2/float-buffer support is detected; existing visuals remain the fallback

UI

• new Fluid field toggle
• Fluid response: Soft / Balanced / Expressive
• settings persist with the other Visuals preferences
• version bumped to 0.2.0

Maintenance

• fluid solver isolated in src/fluid.js
• no changes to connection, setup parsing, sidebar behavior or the Three.js viewer
• MIT attribution added to THIRD_PARTY_LICENSES