feat: add six-cylinder V6 engine model and 3D visualization

[mtiller-jh]

Summary

• add a six-cylinder four-stroke V6 engine model with ideal-gas cylinders, Wiebe heat release, intake/exhaust valve profiles, throttle, intake manifold, friction, crankshaft connector, and ideal dynamometer test
• include calibrated wide-open-throttle torque and converged cylinder-pressure visualizations
• add a standalone interactive 3D engine animation with V-bank cylinders, pistons, poppet valves, pressure volumes, corrected crankshaft kinematics, and independently scaled valve-lift traces

Validation

• Dyad compilation completes
• 3,000 RPM dynamometer smoke simulation returns Success
• standalone visualization JavaScript passes node --check