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

src/rendering/terrain_manager.cpp

@@ -705,7 +705,15 @@ bool TerrainManager::advanceFinalization(FinalizingTile& ft) {
         // Load water immediately after terrain (same frame) — water is now
         // deduplicated to ~1-2 merged surfaces per tile, so this is fast.
         if (waterRenderer) {
+            size_t beforeSurfaces = waterRenderer->getSurfaceCount();
             waterRenderer->loadFromTerrain(pending->terrain, true, x, y);
+            size_t afterSurfaces = waterRenderer->getSurfaceCount();
+            if (afterSurfaces > beforeSurfaces) {
+                LOG_INFO("Water: tile [", x, ",", y, "] added ", afterSurfaces - beforeSurfaces,
+                         " surfaces (total: ", afterSurfaces, ")");
+            }
+        } else {
+            LOG_WARNING("Water: waterRenderer is null during tile [", x, ",", y, "] finalization!");
         }
 
         // Ensure M2 renderer has asset manager