refactor(ui): modularize instance shell

Split InstanceShell2 into focused shell modules (drawer chrome/resize, session context/cache, sidebar, right panel tabs/components) to improve maintainability while preserving behavior.

packages/ui/src/components/instance/shell/useGlobalPointerDrag.ts

@@ -0,0 +1,29 @@
+type GlobalPointerDragHandlers = {
+  onMouseMove: (event: MouseEvent) => void
+  onMouseUp: (event: MouseEvent) => void
+  onTouchMove: (event: TouchEvent) => void
+  onTouchEnd: (event: TouchEvent) => void
+}
+
+type GlobalPointerDrag = {
+  start: () => void
+  stop: () => void
+}
+
+export function useGlobalPointerDrag(handlers: GlobalPointerDragHandlers): GlobalPointerDrag {
+  const start = () => {
+    document.addEventListener("mousemove", handlers.onMouseMove)
+    document.addEventListener("mouseup", handlers.onMouseUp)
+    document.addEventListener("touchmove", handlers.onTouchMove, { passive: false })
+    document.addEventListener("touchend", handlers.onTouchEnd)
+  }
+
+  const stop = () => {
+    document.removeEventListener("mousemove", handlers.onMouseMove)
+    document.removeEventListener("mouseup", handlers.onMouseUp)
+    document.removeEventListener("touchmove", handlers.onTouchMove)
+    document.removeEventListener("touchend", handlers.onTouchEnd)
+  }
+
+  return { start, stop }
+}