V80 DEPTH EFFICIENCY RETUNE

Base
- Starts from V79: secondary deformation disabled, 564,426 coast fix preserved, Shimonoseki/Kanmon 332,225 10% damping preserved, coast absorb fix preserved.

Depth efficiency change
- Thrust/reverse tsunami depth factor is no longer 100% for all depths shallower than 20 km.
- New shallow behavior:
  * 0 km  -> 100%
  * 0-20 km -> linear decay
  * 20 km -> 70%
- After 20 km, the previous S-shaped moderate-depth attenuation style is kept, but normalized from 70% at 20 km to 15% at 80 km.
- 80+ km behavior is unchanged: 15% at 80 km, decaying to about 0.5% near 150 km.

Formula summary
- d <= 20: factor = 1.0 - 0.30 * (d / 20)
- 20 < d <= 80: old logistic shape, remapped 0.70 -> 0.15
- d > 80: old exponential tail
