V144 visible depth export compile fix

- Fixes MinGW compile error in tsunami_gui_win32.c: jesim_observation_cell_shoreline_equiv_height().
- Exposes visible_effective_depth_m() through tsunami_core.h instead of keeping it file-static inside tsunami_core.c.
- Keeps v143 behavior: map/max wave use no output shoaling multiplier; station/JESIM keep 1 m shoreline-equivalent conversion.
- No physics constants changed.
