V89 GLOBAL 6-HOUR DECAY = 6%

Base
- Starts from V88, which disabled the whole-field 6-hour decay.

Change
- Restores mild global wave-height decay.
- GLOBAL_HEIGHT_DECAY_KEEP_6H = 0.940.
- This means wave amplitude loses about 6% every 6 simulated hours.
- The per-step decay is adjusted for WAVE_INTERNAL_SUBSTEPS so two internal substeps together still equal the intended displayed-time decay.

Preserved
- v87 stable 2x internal substeps
- v85 depth-speed exponent fix
- v84 Petal settings removed
- secondary deformation disabled
- Shimonoseki/Kanmon choke cell at 332,225
- coast absorb fix
