Improve water waves, shore effects, and reflections

[vanlueckn]

Summary

• Add depth- and shoreline-aware water rendering data, including assumed depth profiles for surface-only elevation data.
• Replace the basic wave shader with multi-octave directional waves, river flow, refraction, screen-space reflections, foam, spume, rain rings, and glitter.
• Add depth prepasses to the main and route-editor cameras for water reflections.
• Keep foliage alpha masks compatible with depth prepasses by removing the alpha-to-coverage switch.
• Expand water mesh tests for shoreline distance, tile seams, assumed depth, and vertex color data.

Testing

• Not run; changes were reviewed from the supplied diff only.
• Recommended: run the Rust workspace test suite, including content and world-render unit tests.
• Recommended: launch the app and route editor to verify water reflections, shore foam, rivers, foliage depth, and water-body rendering across tile seams.