Fix water descriptor pool leak and add water rendering diagnostics

- Add VK_DESCRIPTOR_POOL_CREATE_FREE_DESCRIPTOR_SET_BIT to water material
  descriptor pool so individual sets can be freed when tiles are unloaded
- Free descriptor sets in destroyWaterMesh() instead of leaking them
- Add terrain manager unloadAll() during logout to properly clear stale
  tiles, water surfaces, and queues between sessions
- Add diagnostic logging for water surface loading, material allocation
  failures, and render skip reasons to investigate missing water

include/rendering/water_renderer.hpp

@@ -172,6 +172,7 @@ private:
     VkImageView sceneDepthView = VK_NULL_HANDLE;
     VkExtent2D sceneHistoryExtent = {0, 0};
     bool sceneHistoryReady = false;
+    mutable uint32_t renderDiagCounter_ = 0;
 
     // Planar reflection resources
     static constexpr uint32_t REFLECTION_WIDTH = 512;