Fix wall-climbing behavior of fluid particles near flask sides

[Testtesttestestes]

Motivation

• Particles were sometimes creeping upward along the flask walls under motion due to excessive tangential wall traction and strong tangential coupling on near-vertical walls.
• Reduce wall-driven tangential forces so fluid respects gravity while preserving coherent near-wall flow and wave slip behavior.

Description

• Adjusted the wall contact viscous term in src/sph/update.frag by reducing the side tangential scale from mix(1.0, 0.35, ...) to mix(1.0, 0.15, ...) to lower tangential viscous pull on near-vertical walls.
• Added a sideWallSlipCoupling factor and attenuated wallVel/wallSlip for side walls, applying cohesive wave slip after this coupling so slip remains but cannot pull particles upward unnaturally.
• Changes are localized to calcAcceleration() and the contact resolution block in src/sph/update.frag and preserve existing restitution/damping logic.

Testing

• Ran npm run build and the production build completed successfully.
• Started the dev server with npm run dev and performed a visual validation; a Playwright screenshot was captured (artifacts/progressbar-fix.png) showing the updated behavior.

---

Codex Task