test(10-05): Wave 0 keyboard + OS-drag + drag-to-move stubs (UX-05..09, UX-11)

- keyboard.test.js: 11 it.todo stubs for UX-05 search focus, UX-06 escape clear, UX-07 upload picker, UX-08 new folder
- OsDragOverlay.test.js: 7 it.todo stubs for UX-09 OS file drag overlay depth-counter + teleport
- StorageBrowser.dragmove.test.js: 6 it.todo stubs for UX-11 drag-to-move ring highlight + toast wiring

frontend/src/components/layout/__tests__/OsDragOverlay.test.js

@@ -0,0 +1,11 @@
+import { describe, it } from 'vitest'
+
+describe('UX-09: OsDragOverlay shows when OS files are dragged over the window', () => {
+  it.todo('overlay hidden by default (dragDepth=0)')
+  it.todo('dragenter with dataTransfer.types including "Files" shows overlay')
+  it.todo('dragenter without "Files" type is ignored (in-app element drag)')
+  it.todo('dragleave decrements depth; overlay hides when depth reaches 0')
+  it.todo('drop event emits files-dropped with the file list')
+  it.todo('drop resets dragDepth to 0 and hides overlay')
+  it.todo('overlay is teleported to body with z-[9998] (below toast z-[9999])')
+})