P50-P56 — six more case studies (12 → 18 installations)

[harsh-pandhe]

Use tools/new_case_study.py (P49) to scaffold each:

• P50 Mexico City Cablebús Línea 1
• P51 Caracas Metrocable San Agustín
• P52 Bogotá TransMiCable
• P53 Second funitel (3 Vallées)
• P54 Reversible 3S over a fjord (needs P48 bathymetry)
• P55 High-altitude Andean line
• P56 Documented ice-event line

Each: feasible + as-built compare; bumps the validation count from 12 → 18.