feat: 任务栏图标嵌入、窗口置顶钉子与进程资源采样

- build.rs + embed-resource 嵌入 icon.ico：gpui 从 exe 资源 ID 1
  加载窗口类图标，此前缺失导致任务栏显示系统默认图标
- 标题栏新增钉子按钮：sysmon::set_topmost 经 raw-window-handle
  取 HWND 调 SetWindowPos(HWND_TOPMOST)，Pin/PinOff 图标随状态切换
- sysmon 模块：CPU 时间差分、工作集/峰值/提交内存、线程/句柄采样
  与运行时长基准（Windows 实现，其余平台返回空采样）

gpui-app/Cargo.toml

@@ -52,3 +52,18 @@ sentry = { version = "0.49", default-features = false, features = [
     "reqwest",
     "rustls",
 ] }
+
+# 窗口置顶（raw HWND + SetWindowPos）与进程资源采样
+raw-window-handle = "0.6"
+[target.'cfg(target_os = "windows")'.dependencies]
+windows = { version = "0.58", features = [
+    "Win32_Foundation",
+    "Win32_System_Threading",
+    "Win32_System_ProcessStatus",
+    "Win32_System_Diagnostics_ToolHelp",
+    "Win32_UI_WindowsAndMessaging",
+] }
+
+# 嵌入窗口图标（gpui 从 exe 资源 ID 1 加载，缺失则任务栏显示默认图标）
+[target.'cfg(target_os = "windows")'.build-dependencies]
+embed-resource = "3"