Fix GPU resource leaks and re-entrant world loading for instance transitions

Reset descriptor pools in CharacterRenderer/M2Renderer/WMORenderer on map
change to prevent VK_ERROR_DEVICE_LOST from pool exhaustion. Defer re-entrant
SMSG_NEW_WORLD during active world load to avoid recursive cleanup crashes.
Gate swim bubbles on swimming state, skip redundant shadow pipeline re-init,
add WOWEE_SKIP_* env vars for render isolation debugging.

include/rendering/character_renderer.hpp

@@ -48,6 +48,7 @@ public:
                     VkRenderPass renderPassOverride = VK_NULL_HANDLE,
                     VkSampleCountFlagBits msaaSamples = VK_SAMPLE_COUNT_1_BIT);
     void shutdown();
+    void clear();  // Remove all models/instances/textures but keep pipelines/pools
 
     void setAssetManager(pipeline::AssetManager* am) { assetManager = am; }