fix(rendering): wait all frame fences before freeing shared descriptor sets

deferAfterFrameFence only waits for one frame slot's fence, but shared
resources (material descriptor sets, vertex/index buffers) are bound by
both in-flight frames' command buffers. On AMD RADV this caused
vkFreeDescriptorSets errors and eventual SIGSEGV.

Add deferAfterAllFrameFences: queues to every frame slot with a shared
counter so cleanup runs exactly once, after the last slot is fenced.
Use it for WMO, terrain, water, and character model shared resources.
Per-frame bone sets keep using deferAfterFrameFence (already correct).

Also fix character renderer vertex format: R8G8B8A8_UINT -> _SINT to
match shader's ivec4 input (RADV validation rejects the mismatch).

include/rendering/vk_context.hpp

@@ -65,6 +65,10 @@ public:
     // be referenced by command buffers submitted in the previous frame(s),
     // such as descriptor sets and buffers freed during streaming/unload.
     void deferAfterFrameFence(std::function<void()>&& fn);
+    // Like deferAfterFrameFence, but waits until ALL in-flight frame slots have
+    // been fenced — safe for shared resources bound by multiple frames' command
+    // buffers (material descriptor sets, vertex/index buffers, etc.).
+    void deferAfterAllFrameFences(std::function<void()>&& fn);
 
     // Accessors
     VkInstance getInstance() const { return instance; }