V88 DISABLE GLOBAL 6-HOUR DECAY

Base
- Starts from V87 stable 2x internal substeps.

Change
- Whole-field global 6-hour decay is disabled:
  global_height_decay_per_step() now returns 1.0f.

Still active
- Hidden outer absorber
- Coast reflection / coast absorb
- Shimonoseki/Kanmon choke-cell damping at 332,225
- Local bathymetry/propagation effects
- v85 depth-speed exponent fix
- v87 stable internal substep speed-up

Purpose
- Test whether the previous apparent under/over damping was mainly caused by wave speed timing rather than the global 6-hour decay.
