feat: RenderGraph GPU timestamp profiling

- RG::SetQueryPool 可选注入；Execute 期每 pass 前后各写一枚
  writeTimestamp2(BOTTOM_OF_PIPE)，索引按帧槽位分区 + 执行序排布
- 每帧录制开头 reset 本槽位查询区间（上一轮结果已在 fence 等待后读取）
- Renderer 在 WaitFence 后读 64bit 结果换算毫秒（timestampPeriod 缓存），
  经 GetPassNames/GetPassGpuMs 透出给 ImGui 面板显示
- 每槽位首帧跳过读取（查询尚未 primed，避免 VUID-09401）

Engine/src/Renderer/Renderer.cpp

@@ -258,6 +258,19 @@ namespace Engine
         UpdateShadowDescriptors();
         UpdateFullscreenDescriptors();
 
+        // 12. GPU timestamp：每 pass 两枚（前后），按帧槽位分区
+        m_QueriesPerFrame = static_cast<u32>(m_RenderGraph->GetPassCount()) * 2;
+        m_PassNames = m_RenderGraph->GetPassNames();
+        m_PassGpuMs.assign(m_RenderGraph->GetPassCount(), 0.0f);
+
+        vk::QueryPoolCreateInfo qpInfo;
+        qpInfo.setQueryType(vk::QueryType::eTimestamp)
+              .setQueryCount(m_QueriesPerFrame * kMaxFramesInFlight);
+        m_QueryPool = m_Device->GetDevice().createQueryPool(qpInfo);
+        m_RenderGraph->SetQueryPool(m_QueryPool, m_QueriesPerFrame);
+        m_TimestampPeriod = static_cast<f32>(
+            m_Device->GetPhysicalDevice().getProperties().limits.timestampPeriod);
+
         ENGINE_INFO("Renderer initialized");
     }
 
@@ -294,6 +307,9 @@ namespace Engine
 
         vkDevice.destroySampler(m_ShadowSampler);
         vkDevice.destroySampler(m_TonemapSampler);
+        if (m_QueryPool) {
+            vkDevice.destroyQueryPool(m_QueryPool);
+        }
         vkDevice.destroyPipelineLayout(m_PipelineLayout);
         vkDevice.destroyPipelineLayout(m_ShadowPipelineLayout);
         vkDevice.destroyPipelineLayout(m_TonemapPipelineLayout);
@@ -804,6 +820,37 @@ namespace Engine
         }
     }
 
+    void Renderer::ReadGpuTimes(u32 frameSlot)
+    {
+        if (!m_QueryPool || m_QueriesPerFrame == 0) return;
+
+        // 每槽位首帧：该区间的查询尚未被 reset/写入，跳过一次读取
+        if (!m_TimesPrimed[frameSlot]) {
+            m_TimesPrimed[frameSlot] = true;
+            return;
+        }
+
+        const u32 passCount = m_QueriesPerFrame / 2;
+        std::vector<u64> ticks(m_QueriesPerFrame, 0);
+
+        // fence 已等待本槽位上一轮完成，结果必然可用（阻塞式 + 64bit）
+        const vk::Result r = m_Device->GetDevice().getQueryPoolResults(
+            m_QueryPool,
+            frameSlot * m_QueriesPerFrame, m_QueriesPerFrame,
+            sizeof(u64) * m_QueriesPerFrame,
+            ticks.data(), sizeof(u64),
+            vk::QueryResultFlagBits::e64 | vk::QueryResultFlagBits::eWait);
+        if (r != vk::Result::eSuccess) return;
+
+        for (u32 i = 0; i < passCount; ++i) {
+            const u64 start = ticks[i * 2];
+            const u64 end = ticks[i * 2 + 1];
+            m_PassGpuMs[i] = (end >= start)
+                ? static_cast<f32>(end - start) * m_TimestampPeriod / 1.0e6f
+                : 0.0f;
+        }
+    }
+
     void Renderer::Render(ECS::Scene& scene, Assets::AssetManager& assets)
     {
         m_BoundScene = &scene;
@@ -880,6 +927,7 @@ namespace Engine
         // 此时本槽位的 fence 尚未 reset——先等它（保证 GPU 已完成本槽位上一轮），
         // 再写 UBO，写-读竞争关闭。
         m_SyncManager->WaitFence(frameSlot);
+        ReadGpuTimes(frameSlot);   // fence 已等：上一轮该槽位的查询已就绪
         m_UniformBuffer->Update(frameSlot, &ubo, sizeof(ubo));
         m_SyncManager->ResetFence(frameSlot);